diff --git a/main.c b/main.c
index 4073c75..dc306ea 100644
--- a/main.c
+++ b/main.c
@@ -25,7 +25,6 @@ int main(int argc, char *argv[])
 	int i, c, k = 15, w = -1, b = MM_IDX_DEF_B, n_threads = 3, keep_name = 1, is_idx = 0, is_hpc = 0;
 	int mini_batch_size = 100000000;
 	uint64_t batch_size = 4000000000ULL;
-	float f = 0.001;
 	bseq_file_t *fp = 0;
 	char *fnw = 0;
 	FILE *fpr = 0, *fpw = 0;
@@ -43,7 +42,7 @@ int main(int argc, char *argv[])
 		else if (c == 'd') fnw = optarg; // the above are indexing related options, except -I
 		else if (c == 'r') opt.radius = atoi(optarg);
 		else if (c == 'c') opt.min_cnt = atoi(optarg);
-		else if (c == 'f') f = atof(optarg);
+		else if (c == 'f') opt.mid_occ_frac = atof(optarg);
 		else if (c == 't') n_threads = atoi(optarg);
 		else if (c == 'v') mm_verbose = atoi(optarg);
 		else if (c == 'g') opt.max_gap = atoi(optarg);
@@ -87,7 +86,7 @@ int main(int argc, char *argv[])
 		fprintf(stderr, "    -l         the 1st argument is a index file (overriding -k, -w and -I)\n");
 //		fprintf(stderr, "    -b INT     bucket bits [%d]\n", b); // most users wouldn't care about this
 		fprintf(stderr, "  Mapping:\n");
-		fprintf(stderr, "    -f FLOAT   filter out top FLOAT fraction of repetitive minimizers [%.3f]\n", f);
+		fprintf(stderr, "    -f FLOAT   filter out top FLOAT fraction of repetitive minimizers [%.3f]\n", opt.mid_occ_frac);
 		fprintf(stderr, "    -r INT     bandwidth [%d]\n", opt.radius);
 		fprintf(stderr, "    -c INT     retain a mapping if it consists of >=INT minimizers [%d]\n", opt.min_cnt);
 		fprintf(stderr, "    -L INT     min matching length [%d]\n", opt.min_match);
diff --git a/map.c b/map.c
index 6ef39b1..46c0ae3 100644
--- a/map.c
+++ b/map.c
@@ -11,7 +11,7 @@ void mm_mapopt_init(mm_mapopt_t *opt)
 {
 	opt->n_frag_mini = 100;
 	opt->max_occ_frac = 1e-5f;
-	opt->mid_occ_frac = 1e-3f;
+	opt->mid_occ_frac = 2e-4f;
 	opt->sdust_thres = 0;
 
 	opt->radius = 500;
@@ -108,7 +108,7 @@ int mm_pair_thin_core(mm_tbuf_t *b, uint64_t x, int radius, int rel, int st0, in
 		for (i = st; i < en; ++i) {
 			uint64_t y = z[i];
 			if (((x ^ y) & 1) == rel) {
-				printf("* %d,%d\n", (uint32_t)x>>1, (uint32_t)y>>1);
+//				printf("* %d,%d\n", (uint32_t)x>>1, (uint32_t)y>>1);
 				kv_push(uint64_t, b->km_fixed, *a, y);
 			}
 		}
@@ -148,7 +148,7 @@ void mm_pair_thin(mm_tbuf_t *b, int radius, mm_match_t *m1, mm_match_t *m2)
 	}
 	for (i = 0; i < 2; ++i)
 		m[i]->n = a[i].n, m[i]->x.r = a[i].a, m[i]->is_alloc = 1;
-	printf("%d,%d; %d,%d\n", m[0]->qpos>>1, m[1]->qpos>>1, m[0]->n, m[1]->n);
+//	printf("%d,%d; %d,%d\n", m[0]->qpos>>1, m[1]->qpos>>1, m[0]->n, m[1]->n);
 }
 
 void mm_map_frag(const mm_mapopt_t *opt, const mm_idx_t *mi, mm_tbuf_t *b, uint32_t m_st, uint32_t m_en)
@@ -167,8 +167,10 @@ void mm_map_frag(const mm_mapopt_t *opt, const mm_idx_t *mi, mm_tbuf_t *b, uint3
 		m[i].span = p->x & 0xff;
 		m[i].x.cr = mm_idx_get(mi, p->x>>8, &t);
 		m[i].n = t;
-		if (i) printf("; ");
-		if (mm_verbose >= 5) printf("%d,%d", m[i].qpos>>1, t);
+		if (mm_verbose >= 5) {
+			if (i) printf("; ");
+			printf("%d,%d", m[i].qpos>>1, t);
+		}
 	}
 	if (mm_verbose >= 5) printf("\n");
 
@@ -178,15 +180,26 @@ void mm_map_frag(const mm_mapopt_t *opt, const mm_idx_t *mi, mm_tbuf_t *b, uint3
 		if (m[i].n >= opt->mid_occ) {
 			if (last2 < 0) last2 = i;
 			if (last < 0 || m[last].n < m[i].n) last = i;
-			if (last >= 0 && (m[last].qpos>>1) + (m[last].span>>1) <= m[i].qpos>>1) {
+			if (last >= 0 && (m[last].qpos>>1) + (m[last].span>>0) <= m[i].qpos>>1) {
 				mm_pair_thin(b, opt->radius, &m[last], &m[i]);
 				last2 = last = -1;
-			} else if (last2 >= 0 && (m[last2].qpos>>1) + (m[last2].span>>1) <= m[i].qpos>>1) {
+			} else if (last2 >= 0 && (m[last2].qpos>>1) + (m[last2].span>>0) <= m[i].qpos>>1) {
 				mm_pair_thin(b, opt->radius, &m[last2], &m[i]);
 				last2 = last = -1;
 			}
 		}
 	}
+
+	int n_tot = 0, n_low = 0, s_low = 0;
+	for (i = 0; i < n; ++i) {
+		if (m[i].n > 0) ++n_tot;
+		if (m[i].n > 0 && m[i].n < opt->mid_occ) ++n_low, s_low += m[i].n;
+	}
+	printf("%d\t%d\t%d\t%d\n", n_tot, n_low, s_low, n);
+
+	// free
+	for (i = 0; i < n; ++i)
+		if (m[i].is_alloc) kfree(b->km_fixed, m[i].x.r);
 	kfree(b->km_fixed, m);
 }