diff --git a/lab3/subdivide_grid.cpp b/lab3/subdivide_grid.cpp
index 4df4079..2352b44 100644
--- a/lab3/subdivide_grid.cpp
+++ b/lab3/subdivide_grid.cpp
@@ -147,25 +147,25 @@ void SubdivideMulti_Grid2D(const GRID2D_POINTS3D& grid2D,
 
 // io
 /// construct output name
-static std::string CreateOutputFilename(const std::string& infilename) {
+static std::string CreateOutputFilename(const std::string& infilename, const int num_iter) {
     const std::string grid2d_ext = ".grid2D";
     if (infilename.size() > grid2d_ext.size() &&
         infilename.substr(infilename.size() - grid2d_ext.size()) == grid2d_ext)
     {
         return infilename.substr(0, infilename.size() - grid2d_ext.size())
-               + "-subdiv.grid2D";
+               + "-subdiv-" + std::to_string(num_iter) + ".grid2D";
     }
-    return infilename + "-subdiv.grid2D";
+    return infilename + "-subdiv-" + std::to_string(num_iter) + ".grid2D";
 }
-static std::string CreateOffOutputFilename(const std::string& infilename) {
+static std::string CreateOffOutputFilename(const std::string& infilename, const int num_iter) {
     const std::string grid2d_ext = ".grid2D";
     if (infilename.size() > grid2d_ext.size() &&
         infilename.substr(infilename.size() - grid2d_ext.size()) == grid2d_ext)
     {
         return infilename.substr(0, infilename.size() - grid2d_ext.size())
-               + "-subdiv.off";
+               + "-subdiv-" + std::to_string(num_iter) + ".off";
     }
-    return infilename + "-subdiv.off";
+    return infilename + "-subdiv-" + std::to_string(num_iter) + ".off";
 }
 
 void UsageMsg(const std::string& command_name) {
@@ -219,7 +219,7 @@ int main(int argc, char* argv[]) {
     SubdivideMulti_Grid2D(grid2D, result, num_iter);
 
     // Write grid2D output.
-    const std::string outfilename = CreateOutputFilename(infilename);
+    const std::string outfilename = CreateOutputFilename(infilename, num_iter);
     const std::vector<std::string> comments = {
         "Subdivided grid. Iterations: " + std::to_string(num_iter),
         "Input: " + infilename
@@ -236,7 +236,7 @@ int main(int argc, char* argv[]) {
 
     // Optionally write .off output.
     if (write_off) {
-        const std::string off_outfilename = CreateOffOutputFilename(infilename);
+        const std::string off_outfilename = CreateOffOutputFilename(infilename, num_iter);
         WRITE_GRID2D_OFF writeOFF;
         const std::vector<std::string> off_comments = {
             "Subdivided grid in OFF format. Iterations: " + std::to_string(num_iter),