diff --git a/bin/ftsort/ftsort.cpp b/bin/ftsort/ftsort.cpp
index 2f473a1..2b87f55 100644
--- a/bin/ftsort/ftsort.cpp
+++ b/bin/ftsort/ftsort.cpp
@@ -30,6 +30,10 @@ size_t get_mem_peak() {
     return mem;
 }
 
+// if we assume N as INPUT tape size, we can calucalte the optimal memory-limit
+// by using this formula:
+// X = sqrt(8000*N)
+// where X is the optimal memory-limit value
 int main(int argc, char *argv[]) {
     AppSettings settings = parse_command_line(argc, argv);
     if (settings.version) {