diff --git a/conv/aprob_bmap.cc b/conv/aprob_bmap.cc
index 489f61f..b9d3607 100644
--- a/conv/aprob_bmap.cc
+++ b/conv/aprob_bmap.cc
@@ -17,11 +17,14 @@ HelpFlag help {
   parser, "help", "display this menu", {'h', "help"},
 };
 
-ValueFlag<double> min {
-  parser, "0.2", "minimum alter-probability to select", {"min"}, 0.4,
+ValueFlag<double> mid {
+  parser, "probability", "desired value of alter-probability to select", {"mid"}, 0.5,
 };
-ValueFlag<double> max {
-  parser, "0.6", "maximum alter-probability to select", {"max"}, 0.6,
+ValueFlag<double> max_dist {
+  parser, "max distance", "maximum distance from mid value", {"max-dist"}, 0.2,
+};
+ValueFlag<uint32_t> min_bnum {
+  parser, "number of blocks", "minimum number of blocks to select (prior than max-dist)", {"min-bnum"}, 32,
 };
 
 }  // namespace param
@@ -30,11 +33,25 @@ ValueFlag<double> max {
 static void Exec() {
   const auto aprob = ReadMatrix<double>(std::cin);
 
+  const auto mid      = args::get(param::mid);
+  const auto max_dist = args::get(param::max_dist);
+  const auto min_bnum = args::get(param::min_bnum);
+
+  std::vector<std::pair<size_t, double>> vec;
   for (auto& probs : aprob) {
-    for (size_t i = 0; i < probs.size(); ++i) {
-      if (args::get(param::min) <= probs[i] && probs[i] <= args::get(param::max)) {
-        std::cout << i << ' ';
+    vec.reserve(probs.size());
+    vec.clear();
+    for (auto prob : probs) {
+      vec.emplace_back(vec.size(), std::abs(prob-mid));
+    }
+    std::sort(vec.begin(), vec.end(), [](auto& a, auto& b) { return a.second < b.second; });
+
+    Enforce(vec.size() >= min_bnum, "cannot satisfy min-bnum limitation");
+    for (auto itr = vec.begin(); itr < vec.end(); ++itr) {
+      if (itr >= vec.begin()+min_bnum) {  // min-bnum is satisfied
+        if (itr->second > max_dist) break;  // max-dist is unsatisfied
       }
+      std::cout << itr->first << ' ';
     }
     std::cout << '\n';
   }