hdu 5187 zhx's contest 快速冪，快速乘

答案就是(2^n-2)%p，由於p很大，直接快速冪會爆掉，用個快速乘。

#include<iostream>
#include<cstring>
#include<cstdio>
#include<ostream>
#include<istream>
#include<algorithm>
#include<queue>
#include<string>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<vector>
#define fi first
#define se second
#define ll long long
#define pii pair<int,int>
#define inf (1<<30)
#define eps 1e-8
#define pb push_back
using namespace std;
const int maxn=110005;
ll n,p;
ll mul(ll a,ll b)
{
    if(b==0)
        return 0;
    ll ans=mul(a,b/2);
    ans=(ans+ans)%p;
    if(b&1)
        ans=(ans+a)%p;
    return ans;
}
ll powMod(ll a,ll b)
{
    if(b==0) return 1;
    ll ans=powMod(a,b/2);
    ans=mul(ans,ans);
    if(b&1)
        ans=mul(ans,a);
    return ans;
}
int main()
{
    while(~scanf("%I64d%I64d",&n,&p)) {
        ll ans=(powMod(2,n-1)-2+p)%p*2%p;
        ans=(ans+2)%p;
        printf("%I64d\n",ans);
    }
    return 0;
}