#include <bits/stdc++.h>
using namespace std;
const int inf = (int)1e9;
const int mod = inf + 7;
const double pi = acos(-1.0);
const double eps = 1e-9;
double rr, r, xa, ya, xb, yb;
int ans;
int main() {
  cin >> r >> xa >> ya >> xb >> yb;
  double d = sqrt((xa - xb) * (xa - xb) + (ya - yb) * (ya - yb));
  long long d1 = (int)d;
  if (d - d1 < eps && d1 % 2 == 0)
    cout << d1 / (r + r);
  else
    cout << d1 / (r + r) + 1;
  return 0;
}
