P1447 [NOI2010] 能量采集

題目:

#include <bits/stdc++.h>
using namespace std;
long long pri(int n)
{
    long long ans=n;
    for(int i=2;i<=n/i;i++)
    {
        if(n%i==0)
        {
            ans=(long long)ans*(i-1)/i;
            while(n%i==0) n/=i;
        }
    }
    if(n>1) ans=(long long)ans*(n-1)/n;
    return ans;
}
int main()
{
    int n,m;
    cin>>n>>m;
    unsigned long long ans=0;
    int x=min(n,m);
    for(int i=1;i<=x;i++)
    {
        long long g=pri(i);
        ans+=(long long)g*(n/i)*(m/i);
    }
    ans=(long long)2*ans-(long long)n*m;
    cout<<ans<<endl;
    return 0;
}