#include<bits/stdc++.h> using namespace std; long long f[55]; int main(){ int n; cin>>n; f[1]=3; f[2]=6; f[3]=6; for(int i=4;i<=n;i++){ f[i]=f[i-1]+f[i-2]*2; } if(n==1)cout<<0; else{ cout<<f[n]; } return 0; }

#include<iostream> using namespace std; int main(){ int n; cin>>n; long long a[1001]; a[1]=0; a[2]=6; for(int i=3;i<=n;i++){ a[i]=a[i-1]+2*a[i-2]; } cout<<a[n];//懂的都懂 return 0; }

#include<bits/stdc++.h> using namespace std; int main(){ int n; cin >> n; long long a[50] = {}; a[1] = 0, a[2] = 6, a[3] = 6; for(int i = 4; i <= n; i++){ a[i] = a[i-1] + a[i-2] * 2; } cout << a[n]; return 0; }