#include <stdio.h>
#include <math.h>
#include <string.h>

long long ji(long long l, long long r) {
	if ((r - l + 1 ) % 2 == 0)
		return (r - l + 1) / 2;
	else if (l % 2 == 0)
		return (r - l + 1) / 2;
	else
		return (r - l + 1) / 2 + 1;
}

long long bei(long long l, long long r) {
	if (l % 4 == 0 && r % 4 == 0)
		return (r - l + 1) / 4 + 1;
	else if (l % 4 == 0 || r % 4 == 0)
		return (r - l + 1) / 4 ;
	else
		return (r - l + 1) / 4 ;
}

int main() {
	long long l, r;
	scanf("%lld%lld", &l, &r);
	printf("%lld", ji(l, r) + bei(l, r));
	return 0;
}
  80分还有20在哪？thanks!!