HDU 4990 Reading comprehension（BestCoder Round #8）

#include<stdio.h>
#include<string.h>
#include<queue>
#include<math.h>
#include<stdlib.h>
#include<algorithm>
using namespace std;

const int N=1e4+10;
const int INF=0x3f3f3f3f;
const int MOD=1e9+7;

typedef long long LL;

LL Solve(LL a, LL b, LL m) ///快速幂
{
    LL t, sum;

    t = a % m;
    sum = 1;

    while (b)
    {
       if(b&1) sum = (sum*t)%m;

       t = (t*t)%m;
       b /= 2;
    }

    return sum;
}

int main ()
{
    LL n, m, ans;

    while (scanf("%lld %lld", &n, &m) != EOF)
    {
        ans = Solve(2, n+1, 3*m);

        if (n % 2 == 0) ans = (ans-2)/3;
        else ans = (ans-1)/3;

        printf("%lld\n", ans);
    }

    return 0;
}