#include <bits/stdc++.h>
using namespace std;
int a[100007];
int main() {
  int n, m, k = 0, l;
  long long ans = 0;
  string s;
  int i = 0, mx = 0, mxii = 0;
  double x, y, xx, yy, r;
  double delta;
  cin >> r >> x >> y >> xx >> yy;
  delta = sqrt((xx - x) * (xx - x) + (yy - y) * (yy - y));
  ans = delta / (2 * r);
  cout << ans << endl;
  return 0;
}
