#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ long long a,b,c=0,i; cin>>a>>b; for(i=a;i<=b;i++) { c+=i; } cout<<c; return 0; }