代码：``` #include <bits/stdc++.h> using namespace std; const int N=1e5+10; int a[N]; int main(){ int n,k,ans=0; cin>>n>>k; for(int i=1;i<=n;i++){ cin>>a[i]; } a[k]=-1*a[k]; for(int i=1;i<=n;i++){ ans+=a[i]; } cout<<ans; return 0; }

[RE×19](https://www.luogu.com.cn/record/113136920)