#include <bits/stdc++.h>   using namespace std;   using ll = long long int;   using ull = unsigned long long int;   using dd = double;   using ldd = long double;   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     ll n, r;     cin >> n >> r;     vector<ll> arr((ll(1)) << n);     ll sum = 0;     n = ((ll)1) << n;     for (int i = 0; i < n; ++i) {       cin >> arr[i];       sum += arr[i];     }     cout.precision(10);     cout << ((dd)sum) / (dd(n)) <<   n ;     for (int i = 0; i < r; ++i) {       ll a, b;       cin >> a >> b;       sum -= arr[a];       sum += b;       arr[a] = b;       cout << ((dd)sum) / (dd(n)) <<   n ;     }   }   