#include<bits/stdc++.h>
typedef long long ll;
using namespace std;
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr); ll n,m;
    cin>>n>>m;
    cout<<(n+m)*(m-n+1)/2;
    return 0;
}

#include<iostream>
using namespace std;
int main()
{
int n,d,sum=0;
cin>>n>>d;
for(int i=n;i<=d;i++)
{
sum=sum+i;

}
cout<<sum;
return 0;
}

#include<iostream>
using namespace std;
int main()
{
int a,b,sum=0;
cin>>a>>b;
for(int i=a;i<=b;i++){
sum+=i;
}
cout<<sum<<endl;
return 0;
}

#include<iostream>
using namespace std;
int s,m,sum=0;
int main()
{
cin>>s>>m;
for(;s<=m;s++)
sum=sum+s;
cout<<sum;
}

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