/*
TASK:rprimes
LANG:C++
*/

#include<stdio.h>

typedef unsigned long long ull;

int rprimes[1000] = {2,3,5,7,23,29,31,37,53,59,71,73,79,233,239,293,311,313,317,373,379,593,599,719,733,739,797,2333,2339,2393,2399,2939,3119,3137,3733,3739,3793,3797,5939,7193,7331,7333,7393,23333,23339,23399,23993,29399,31193,31379,37337,37339,37397,59393,59399,71933,73331,73939,233993,239933,293999,373379,373393,593933,593993,719333,739391,739393,739397,739399,2339933,2399333,2939999,3733799,5939333,7393913,7393931,7393933,23399339,29399999,37337999,59393339,73939133};

int main() {
	int a, b;
	scanf("%i%i", &a, &b);
	int i = 0, num = 0;
	while(rprimes[i] < a) i++;
	while(rprimes[i] <= b) {
		num++;
		i++;
	}
	printf("%i\n", num);
	return 0;
}
