题目大意：已知n个数的平均值m以及前n-1个数，请问第n个数是多少？

#include <stdio.h>
int n, m, i, j, k, s;
int main(){
    scanf("%d", &n);
    for(i=1; i<n; i++){
        scanf("%d", &k);
        s += k;
    }
    scanf("%d", &m);
    printf("%lld\n", (long long)m*n-s);
    return 0;
}