[bzoj1257][CQOI2007]余数之和sum

#include<iostream>
#include<cstdio>
#define ll long long
using namespace std;
int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘) f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘; ch=getchar();}
    return x*f;
}

ll n,k,l,r;
ll ans=0;

int main()
{
    k=read();r=n=read();if(k>n)ans=(k-n)*n,k=n;
    for(int i=1;;i=n/(l-1))
    {
        l=n/(i+1)+1;if(l==1)break;r=n/i;
        if(l<=k) r=min(r,k),ans+=(n%l+n%r)*(r-l+1)/2;
    }
    cout<<ans;
    return 0;
}