Ni Yuan (too many people use me to add these words)

Life is not easy, let me sigh first!
Hey, I didn't understand Ni Yuan before.
"Ah, what did I do with this question"
xx: "Because you didn't know
how to write the question " xx: "Because you don't know how to write the question " ...
51nod topic link portal
1: Nigen
: It
is better written by someone else, wonderful hahaha, other people's home Good blog
Fermat's little theorem:
Fermat's little theorem

The meaning of the title is as above

.

#include <cstdio>
#include <cstring>
#include <string>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <queue>
#include <map>
#include <set>
using namespace std;
typedef long long ll;
const ll mod = 1e9 + 7;
ll n;

ll qpow(ll x, ll y){
    
    
	ll res = 1;
	while(y){
    
    
		if(y & 1){
    
    
			res = res * x % mod;
		}
		y >>= 1;
		x = x * x % mod;
	}
	return res % mod;	
}

int main(){
    
    
	cin >> n;
	ll ans = 0;
	ans = (qpow(3, n + 1) - 1) % mod;
	ans *= qpow(2, mod - 2) % mod;
	ans %= mod;
	cout << ans << endl;
	return 0;
}

I went to write a few questions about the inverse element with enthusiasm, 5555555TLE
. I was shocked to find that I was a fool. There are several ways to find the inverse element.