zj c874 雪花片片

#include <bits/stdc++.h>
using namespace std;

int main(){
    int n; cin>>n;
    n -= 1;
    
    unsigned long long tri[120], side[120];
    tri[0] = 1;
    side[0] = 3;
    
    for(int i=1; i<=n; i++){
        tri[i] = tri[i-1] + side[i-1];
        side[i] = side[i-1]*4;
    }
    
    unsigned long long ans=0;
    for(int i=0; i<n+1; i++){
        ans += tri[i];
        // cout<<ans<<endl;
    }
    
    cout<<ans;
}