#include<stdio.h>

int main() {
    int start, end, sum = 0;
    
    scanf("%d", &start);
    scanf("%d", &end);
    
    if (start > end) {
        printf("Invalid input\n");
        return 0;
    }
    for (int i = start; i <= end; i++) {
        sum  += i;
    }
    
    printf("%d\n", sum");
    
    return 0;
}