#include <bits/stdc++.h>
using namespace std;
long long int MOD = 1000000007;
long long int inf = 1e15;
void scan(int &x);
long long int powermod(long long int _a, long long int _b, long long int _m) {
  long long int _r = 1;
  while (_b) {
    if (_b % 2 == 1) _r = (_r * _a) % _m;
    _b /= 2;
    _a = (_a * _a) % _m;
  }
  return _r;
}
long long int string_to_number(string s) {
  long long int x = 0;
  stringstream convert(s);
  convert >> x;
  return x;
}
long long int add(long long int a, long long int b) {
  long long int x = (a + b) % MOD;
  return x;
}
long long int mul(long long int a, long long int b) {
  long long int x = (a * b) % MOD;
  return x;
}
long long int sub(long long int a, long long int b) {
  long long int x = (a - b + MOD) % MOD;
  return x;
}
long long int divi(long long int a, long long int b) {
  long long int x = a;
  long long int y = powermod(b, MOD - 2, MOD);
  long long int res = (x * y) % MOD;
  return res;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long int n;
  cin >> n;
  long long int m;
  cin >> m;
  long double sum[m], mul[m];
  long double sumdmin = 0.0;
  long double sumdmax = 0.0;
  if (n != 1) {
    if (n % 2 == 0) {
      long long int left = n / 2;
      long long int right = n / 2 - 1;
      sumdmin += (((left) * (left + 1)) / 2);
      sumdmin += (((right) * (right + 1)) / 2);
    } else {
      long long int left = n / 2;
      long long int right = n / 2;
      sumdmin += (((left) * (left + 1)) / 2);
      sumdmin += (((right) * (right + 1)) / 2);
    }
    sumdmax = ((n) * (n - 1)) / 2;
  } else {
    if (n == 1) {
      sumdmin = 0.0;
      sumdmax = 0.0;
    }
  }
  long double suma = 0.0;
  for (int i = 0; i < m; i++) {
    cin >> sum[i] >> mul[i];
    if (mul[i] < 0) {
      suma += ((long double)n * sum[i] + mul[i] * sumdmin);
    } else {
      suma += ((long double)n * sum[i] + mul[i] * sumdmax);
    }
  }
  cout << fixed << setprecision(12);
  cout << suma / (long double)n;
  return 0;
}
