#include <bits/stdc++.h>
using namespace std;
const int MOD = (int)1e9 + 7;
const int N = (int)1e6 + 2829;
const long long INF = (long long)1e18;
const double eps = (double)1e-9;
const int inf = (int)1e9 + 338;
int _sum_(int x) { return x * (x + 1) / 2; }
double x, y, x2, y2, r;
int main() {
  int cnt = 0;
  cin >> r >> x >> y >> x2 >> y2;
  int lin = sqrt((x - x2) * (x - x2) + (y - y2) * (y - y2));
  while (lin > 0) {
    cnt++;
    lin -= (r * 2);
  }
  cout << cnt;
  return 0;
}
