#include <stdio.h>

int main() {
    int n1,n2,v,s;
    v=0;
    scanf("%d %d", &n1,&n2);

    for (int i=n1; i<=n2; i++){

        if (i%2!=0){
            v=i+v;

        }


    }
printf("%d",v);
    return 0;
}