const ll N = 4e7;
ll a[N];
ll b[N];  

ll cnt=0;

int ols(ll n)  //欧拉筛
{
	a[0]=1;
    a[1]=1;
    ll sum=0;

	ll i,j;
	for(i=2;i<=n;i++)
	{
		if(a[i]==0) b[cnt++]=i;
		for(j=0;j<cnt;j++)
		{
			if(b[j]*i>n) break;
			a[b[j]*i]=b[j];
			if(i%b[j]==0) break;
		}
	}
	return 0;
}