#include <stdio.h>

int main() {
    int start_value;
    int end_value;
    long long total_sum = 0;
    
    if (scanf("%d", &start_value) != 1) {
    return 1;
    }
    if (scanf("%d", &end_value) != 1) {
        return 1;
    }
    if (start_value > end_value) {
        print("Invalid Input\n");
        return 0;
    }
    for (int i = start_value; i <= end_value; i++) {
        total_sum += i;
    }
    print("lld\n", total_sum);
    
    return 0;
}