codeforces 584b 超大型指数乘法取模o(logn)

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <cstdlib>
using namespace std;

typedef long long ll;
const ll mod = 1e9 + 7;

ll quick_mod(ll a, ll b) {  
    ll ans = 1;  
    while(b) {  
        if(b&1) ans = (ans * a) % mod;  
        b >>= 1;  
        a = (a * a) % mod;  
    }  
    return ans;  
}  

int main() {
    ll n;
    scanf("%lld", &n);
    ll A = quick_mod(27, n);
    ll B = quick_mod(7, n);
    printf("%lld\n", ((A % mod - B % mod) + mod) % mod);
    return 0;
}