cf992 C. Nastya and a Wardrobe

#include<bits/stdc++.h>
using namespace std;
const int MOD=(int)1e9+7;
typedef long long ll;
ll poww(ll a, ll b)
{
    ll ans = 1, base = a%MOD;
    while(b != 0)
    {
        if(b&1 != 0)
            ans = (ans*base)%MOD; 
        base = (base*base)%MOD;
        b >>= 1;
    }
    return ans%MOD;
}
int main()
{
    ll x,k;
    scanf("%lld%lld",&x,&k);
    if(x==0)
    {
        printf("0
");//注意样例中的特殊范围，看样例中是否包含0！！ 
        return 0;
    }
    x%=MOD;
    printf("%lld
",(x*poww(2,k+1)%MOD-poww(2,k)%MOD+MOD+1)%MOD);//避免减出负数 
}