注意点：
- p也要开long long.
#include<cstdio>
#include<iostream>
#define ll long long
using namespace std;
ll p;
ll mull(ll a,ll b){
ll ans=0,tmp=a;
while(b){
if(b&1)ans=(ans+tmp)%p;
tmp=(tmp+tmp)%p;
b>>=1;
}
return ans;
}
int main(){
ll a,b;
scanf("%lld%lld%lld",&a,&b,&p);
ll ans=mull(a,b);
printf("%lld
",ans);
return 0;
}