#include <bits/stdc++.h>
using namespace std;
int main() {
  double a, b, c, d, r;
  scanf("%lf%lf%lf%lf%lf", &r, &a, &b, &c, &d);
  int ans = ceil(sqrt((a - c) * (a - c) + (b - d) * (b - d)) / r);
  if (ans == 0)
    printf("0\n");
  else
    printf("%d\n", (ans + 1) / 2);
  return 0;
}
