NOI2010 能量采集

#include <cstdio>
#include <iostream>
using namespace std;
const int MAXN = 100000 + 123;
long long cnt[MAXN];
int main()
{
long long n, m;
cin >> n >> m;
int t = n > m ? m : n;

for(int i = 1; i <= t; i++) cnt[i] = (n / i) * (m / i);

long long ans = 0;

for(int i = t; i >= 1; i--)
{
for(int j = 2; j * i <= t; j++)
cnt[i] -= cnt[j * i];
ans += cnt[i] * i;
}

//printf("%I64d\n", 2 * ans - (long long)n * m);
ans = 2 * ans - n * m;
cout << ans << endl;
return 0;
}