#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast")
constexpr ll INF = 1e18;
constexpr int inf = 1e9;
constexpr ll mod = 1000000007;
constexpr ll mod2 = 998244353;
const double PI = 3.1415926535897932384626433832795028841971;
const int dx[6] = {1, 0, -1, 0, 1, 1};
const int dy[6] = {0, 1, 0, -1, 1, -1};
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll N, M;
  cin >> N >> M;
  ll ans = 0;
  if (N == 1) {
    for (int i = 0; i < M; i++) {
      ll a, b;
      cin >> a >> b;
      ans += a;
    }
    cout << ans << '\n';
    return 0;
  }
  ll mn, mx;
  mx = ((N - 1LL) * N) / 2LL;
  mn = (((N / 2LL) + 1LL) * (N / 2LL)) / 2LL;
  mn *= 2LL;
  if (N % 2 == 0) {
    mn -= N / 2LL;
  }
  for (int i = 0; i < M; i++) {
    double a, b;
    cin >> a >> b;
    ans += a * N;
    if (b < 0) {
      ans += b * max(0LL, mn);
    } else {
      ans += b * mx;
    }
  }
  double suzu = double(ans) / double(N);
  cout << fixed << setprecision(20) << suzu << '\n';
  return 0;
}
