[OpenJudge-NOI]神奇序列求和

代码

#include <cstdio>#include <iostream>#include <cstring>using namespace std;int x,y,n,ans(0);int main() {    cin>>x>>y>>n;    ans=x+y;    for(int i=1;i<=n;i++) ans=ans*3-(x+y);    cout<<ans<<endl;}