#include<iostream> #include<cstdio> //scanf()\printf() #include<cstring> #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int n,m,sum=0; cin>>n>>m; for(int i=n;i<=m;i++){ sum+=i; } cout<<sum; return 0; }