#include<bits/stdc++.h> using namespace std; int main(){ int n,m,k; cin>>n>>m>>k; cout<<(n+m)*k/2; return 0; }

参考代码

#include <iostream>
using namespace std;
int main(){

    int a,b,h;
    int s;
    cin>>a>>b>>h;
    s=(a+b)*h/2;
    cout<<s<<endl;
    
    return 0;
}