#include <stdio.h>

int main(void) {
    double ave;
    int A, B, i,c=0;
    
    scanf("%d%d", &A, &B);
    for (i = A; i <= B; i++) {
    	ave = (A + B + i) / 3.0;
    	if (ave == (int)ave) {
    		c++;
    	}
    }
    printf("%d", c);
}