diff --git a/main.cpp b/main.cpp
index d247b91..150f01c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -60,12 +60,30 @@ Pedestrian *init_pedestrians(int n_p) {
 
 int main(int argc, const char *argv[]) {
 
-  Obstacle obs[] = {};
-  Board board = Board(BOARD_LENGTH, BOARD_WIDTH, 0, obs);
+  // Check command line arguments
+  if (argc < 3) {
+    printf("Usage: ./sim <number_of_pedestrians> <number_of_iterations>\n");
+    printf("  number_of_iterations: each iteration = %.2f seconds of simulation time\n", dt);
+    return 1;
+  }
 
+  // Parse command line arguments
   int n_p = atoi(argv[1]);
   int n_iter = atoi(argv[2]);
 
+  if (n_p <= 0) {
+    printf("Error: <number_of_pedestrians> must be a positive integer, got '%s'\n", argv[1]);
+    return 1;
+  }
+
+  if (n_iter <= 0) {
+    printf("Error: <number_of_iterations> must be a positive integer, got '%s'\n", argv[2]);
+    return 1;
+  }
+
+  Obstacle obs[] = {};
+  Board board = Board(BOARD_LENGTH, BOARD_WIDTH, 0, obs);
+
   // Logic to get/dump the simulation data
   const int dump_interval = 50; // dump every 5 iterations -> 20 fps (since dt = 0.01)
   const char *dump_path = (argc >= 4) ? argv[3] : nullptr;
@@ -123,6 +141,9 @@ int main(int argc, const char *argv[]) {
       //
       p.curr_pos = p.curr_pos + p.curr_vel * dt;
 
+      // # 10 flops = 5 ADDs, 2 DIVs, 1 SQRT, 2 MULTs
+      p.e = (p.destination - p.curr_pos) / (p.destination - p.curr_pos).norm();
+
       // how to handle if a pedestrian reached the end of our simulation/end of the hallway
       // The option we do here is to just "teleport" the person back to the beginning
       // the good thing is we will have a constant flow of pedestrians and in the simulation we should see how lines build up
@@ -136,9 +157,6 @@ int main(int argc, const char *argv[]) {
         // p.destination.y = p.curr_pos.y;
       }
 
-      // # 10 flops = 5 ADDs, 2 DIVs, 1 SQRT, 2 MULTs
-      p.e = (p.destination - p.curr_pos) / (p.destination - p.curr_pos).norm();
-
       // if we have a dump path/file we wanna save the data for visualisation
       if (dump_path && (t % dump_interval == 0)) {
         samples.emplace_back(t, i, p.curr_pos.x, p.curr_pos.y, p.color);