#include <bits/stdc++.h>
using namespace std;
void yes() {
  cout << "YES";
  exit(0);
}
void no() {
  cout << "NO";
  exit(0);
}
long long binpow(long long a, long long n) {
  if (n == 0) return 1;
  if (n % 2 == 1)
    return a * binpow(a, n - 1);
  else {
    long long b = binpow(a, n / 2);
    return b * b;
  }
}
struct point {
  long double first, second;
};
int main() {
  long double r;
  point a, b;
  cin >> r >> a.first >> a.second >> b.first >> b.second;
  long double dst = sqrt((a.first - b.first) * (a.first - b.first) +
                         (a.second - b.second) * (a.second - b.second));
  if (dst / r / 2 == int(dst) / r / 2)
    cout << int(dst) / r / 2;
  else
    cout << int(dst / r / 2) + 1;
}
