#include <stdio.h>

int main() {
        int a, b;
        scanf("%d %d", &a, &b);
        int total = 0;
        for (int i = a; i <= b; i=i+2) {
                int n = i + 1;
                if (i % 2 == 1) {
                        n = i;
                } else {
                        if (i == b) {
                                break;
                        }
                }
                //printf("%d\n", n);
                total = total + n;
        }
        printf("%d\n", total);
}