分享答案
#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
double a,b,c;
cin>>a>>b>>c;
cout<<fixed<<setprecision(3)<<(a+b)*c/2<<endl;
return 0;
}
#include<iomanip>
using namespace std;
int main()
{
double a,b,c;
cin>>a>>b>>c;
cout<<fixed<<setprecision(3)<<(a+b)*c/2<<endl;
return 0;
}