# 特以此纪念我自己编写的第一个递归程序
# python中默认的递归深度是1000
def sum(a, b):
    if a == b: return b;
    return a + sum(a + 1, b)

a, b = map(int, input().split())
print(sum(a, b))

#include<iostream>
using namespace std;

int main()
{
int xmin,xmax,num,add;
cin>>xmin>>xmax;
num=(xmax-xmin)/1+1;
add=(xmax+xmin)*num/2;//直接套公式
cout<<add<<endl;
}

#include <iostream>
using namespace std;
int main()
{
    int xmin,xmax;
    cin>>xmin>>xmax;
    int i;
    int ii=i;
    for(ii=xmin;ii<=xmax;ii++)
        i+=ii;
    cout<<i;
    return 0;
}

#include <iostream>
using namespace std;

int main()
{
int max,min,sum;
cin>>max>>min;
sum=(max+min)*(min-max+1)*1/2;
cout<<sum;
return 0;
}

#include <iostream>
using namespace std;
int main()
{
int xmin,xmax,x=0,a;
cin>>xmin>>xmax ;

while(xmin<=xmax)
{
a=xmin;
x=x+a;
xmin=xmin+1;
}

cout<<x<<endl;

return 0;
}

#include<iostream>
using namespace std;
int main()
{
int xmin,xmax,sum;
cin>>xmin>>xmax;
while(xmin <= xmax)
{
sum=xmin+sum;
xmin=xmin+1;
}
cout <<sum<<endl;
return 0;
}