乘法逆元(快速幂)

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#define ll long long
using namespace std;
ll n,p;
int main()
{
    scanf("%lld%lld",&n,&p);
    ll a=n,ans=1,b=p-2;
    while(b)
    {
        if(b&1)
            ans=ans*a%p;
        a=a*a%p;
        b=b>>1;
    }
    printf("%lld",ans);
    return 0;
}