简单数学题

题目链接

推公式

#include <iostream>
#include <cstdio>
using namespace std;
typedef long long ll;
#define mod 1000000007
ll qpow(ll a,ll b){
    ll ans=1;
    a%=mod;
    while(b){
        if(b&1){
            ans=ans*a%mod;
        }
        b/=2;
        a=a*a%mod;
    }
    return ans;
}

int main()
{
    ll n;
    while(~scanf("%lld",&n)){
        ll x=(n-1)%mod;
        ll ans=qpow(2,n);
        ans=((ans*x)%mod+1)%mod;
        cout<<ans<<endl;
    }
    return 0;
}