bzoj2005 [Noi2010]能量采集

#include<bits/stdc++.h>
#define LL long long
#define N 1000000
using namespace std;
LL prime[N+1],siz,phi[N+1];
bool P[N+1];
void init()
{
memset(P,true,sizeof(P));
P[1]=false,phi[1]=1;
for(int i=1;i<=N;i++)
{
if(P[i])
{
prime[++siz]=i;
phi[i]=i-1;
}
for(int j=1;j<=siz&&i<=N/prime[j];j++)
{
P[i*prime[j]]=false;
if(i%prime[j]==0)
{
phi[i*prime[j]]=phi[i]*prime[j];
break;
}
phi[i*prime[j]]=phi[i]*(prime[j]-1);
}
}
}
LL GCD(LL A,LL B)
{
return B==0?A:GCD(B,A%B);
}
int main()
{
//freopen("a.in","r",stdin);
//freopen("a.out","w",stdout)
4000
;
init();
LL Ans=0,m,n;
cin>>m>>n;
for(int i=1;i<=min(m,n);i++)
Ans+=(n/i)*(m/i)*phi[i];
cout<<2*Ans-m*n;
return 0;
}