#include <bits/stdc++.h>
using namespace std;
int n;
double s = 0, a, b[1001];
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a >> b[i];
  for (int i = 1; i <= n; i++) s += b[i];
  printf("%.3lf", (double)s / n + 5);
  return 0;
}
