#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void amin(T &a, U b) {
  a = (a > b ? b : a);
}
template <typename T, typename U>
inline void amax(T &a, U b) {
  a = (a > b ? a : b);
}
void solve() {
  int n, m;
  cin >> n >> m;
  int x[m], y[m];
  int64_t sum = 0;
  vector<int64_t> d(n);
  for (int i = 0; i < n; ++i) {
    int64_t add = (n * 1LL * (n + 1)) / 2 - ((i + 1) * 1LL * i);
    add += (i - (n - i)) * 1LL * (i + 1);
    d[i] = add;
  }
  sort(d.begin(), d.end());
  do {
  } while (0);
  for (int i = 0; i < m; ++i) {
    cin >> x[i] >> y[i];
    int64_t here = x[i] * 1LL * n;
    if (y[i] >= 0)
      here += d.back() * 1LL * y[i];
    else
      here += d[0] * 1LL * y[i];
    sum += here;
  }
  cout << setprecision(6) << fixed;
  cout << (double)sum / n;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int tests = 1;
  while (tests--) {
    solve();
  }
}
