题目链接:http://codeforces.com/problemset/problem/630/H
#include<bits/stdc++.h>using namespace std;#define debug puts("YES");#define rep(x,y,z) for(int (x)=(y);(x)<(z);(x)++)#define ll long long#define lrt int l,int r,int rt#define lson l,mid,rt<<1#define rson mid+1,r,rt<<1|1#define root l,r,rt#define mst(a,b) memset((a),(b),sizeof(a))#define pii pair<int,int>#define fi first#define se second#define mk(x,y) make_pair(x,y)const int mod=1e9+7;const int maxn=1e5+100;const int ub=1e6;ll powmod(ll x,ll y){ll t; for(t=1;y;y>>=1,x=x*x) if(y&1) t=t*x; return t;}ll gcd(ll x,ll y){ if(y==0) return x; return gcd(y,x%y);}ll n,ret=0,ans=0;int main(){ cin>>n;n--; rep(i,1,n+1){ ret=0; if(i==1){ ret=4; if(i+1<=n) ret=ret*3*powmod(4,n-2); }else if(i==n){ ret=4LL*3*powmod(4,n-2); }else{ ret=4LL*3*3*powmod(4,n-3); } ans+=ret; } cout<<ans<<"n"; return 0;}