/*
TASK:rprimes
LANG:C++
*/
#include<iostream>
using namespace std;

int main()
{
    int res[]={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, 2000000000};
    int br=0, i, j, a, b;
    cin >> a >> b;
    for(i=0;;i++)
    {
        if(res[i]>=a)
        {
            if(res[i]>b) break;
            else if(res[i]<=b) br++;
        }
    }
    cout << br << endl;
    system("Pause");
    return 0;
}
        
    
