#include <bits/stdc++.h>   long long sum = 0, dd = 0;   int N, R, V[(1 << 18) + 233];   int main() {     scanf( %d%d , &N, &R);     dd = 1 << N;     for (int i = 0; i < dd; ++i) {       scanf( %d , V + i);       sum += V[i];     }     printf( %.10lf n , sum / (double)dd);     for (int i = 0; i < R; ++i) {       int z, g;       scanf( %d%d , &z, &g);       sum -= V[z];       V[z] = g;       sum += g;       printf( %.10lf n , sum / (double)dd);     }   }   