func_code_string: #include <bits/stdc++.h>   using namespace std;   using LL = long long;   using LD = long double;   const int MX = 1 << 18 | 3;   int N, a[MX], Q;   LL sum;   int main() {     ios::sync_with_stdio(0);     cout << fixed << setprecision(10);     cin >> N >> Q;     for (int i = 0; i < (1 << N); i++) cin >> a[i], sum += a[i];     cout << (LD)sum / (1 << N) <<   n ;     while (Q--) {       int u, x;       cin >> u >> x;       sum = sum - a[u] + x;       a[u] = x;       cout << (LD)sum / (1 << N) <<   n ;     }     return 0;   }   