#include <bits/stdc++.h>
using namespace std;
inline void R(int &x) {
  char ch = getchar();
  x = 0;
  for (; ch < '0'; ch = getchar())
    ;
  for (; ch >= '0'; ch = getchar()) x = x * 10 + ch - '0';
}
const int N = 100005;
double x, y, ans;
int n;
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; ++i) {
    scanf("%lf%lf", &x, &y);
    ans += y;
  }
  printf("%.3lf\n", ans / n + 5);
  return 0;
}
