#include<iostream>
using namespace std;
int main()
{
    int x,y,i,m=0,sum=0;
    cin>>x>>y;
    if(x>y)
    swap (x,y);
    for(i=x+1;i<y;i++)
    {
        sum=sum+i;
        if(i%2==0)
        {m=m+i;}
        else m=m;
    }
     printf("%d\n",(sum-m));
    return 0;
}