#include <bits/stdc++.h>
const int N = 1e6 + 10;
const int mod = 1e9 + 7;
const int INF = 0x3f3f3f3f;
using namespace std;
inline int read() {
  int X = 0;
  bool flag = 1;
  char ch = getchar();
  while (ch<'0' | ch> '9') {
    if (ch == '-') flag = 0;
    ch = getchar();
  }
  while (ch >= '0' && ch <= '9') {
    X = (X << 1) + (X << 3) + ch - '0';
    ch = getchar();
  }
  if (flag) return X;
  return ~(X - 1);
}
double dis(double x1, double y1, double x2, double y2) {
  double dist = fabs(x1 - x2) * fabs(x1 - x2) + fabs(y1 - y2) * fabs(y1 - y2);
  return sqrt(dist);
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  double r, x1, y1, x2, y2;
  cin >> r >> x1 >> y1 >> x2 >> y2;
  double dist = dis(x1, y1, x2, y2);
  int ans = dist / (2 * r);
  if (dist / (2 * r) - ans) ans++;
  cout << ans << endl;
  return 0;
}
