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