#include <bits/stdc++.h>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimization("O2")
#pragma GCC optimization("unroll-loops")
const long double ERR = 1e-5;
const int MOD = 1e9 + 7;
bool areEqual(long double _n1, long double _n2) {
  return fabs(_n1 - _n2) < ERR;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int N;
  cin >> N;
  long double ySUM = 0;
  for (int i = 0; i < N; i++) {
    long double x, y;
    cin >> x >> y;
    ySUM += y;
  }
  cout << fixed << setprecision(3) << 5 + ySUM / N << '\n';
}
