#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() { int n, m, s = 0; cin >> n >> m; for (int i = n; i <= m; i++) { s = i + s; } cout << s; return 0; }