BZOJ 2005 [Noi2010]能量采集

/**************************************************************
Problem: 2005
User: too_weak
Language: C++
Result: Accepted
Time:48 ms
Memory:1588 kb
****************************************************************/

#include <cstdio>
#include <algorithm>
using namespace std;
const int maxn =100005;
typedef long long LL ;
LL f[maxn];///f[i]表示满足gcd(x,y)=i的对数
int main()
{
int n,m;
scanf("%d%d",&n,&m);
LL t=min(n,m);
LL ans=0;
for(int i=t;i;i--){
f[i]=(LL)(m/i)*(n/i);
for(int j=i+i;j<maxn;j+=i)
f[i]-=f[j];
ans+=f[i]*(2*i-1);
}
printf("%lld\n",ans);
return 0;
}