#include <iostream>

using namespace std;

int n;

int prim(int x)
{
    if(x != 2)
        if(x>2 && x%2 == 0)
            return 0;
    for(int i=3;i*i<=x;i+=2)
        if(x%i == 0)
            return 0;
    return 1;
}
int main()
{
    int nr = 0;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for(int i=2;i<=n;i++)
        if(prim(i) == 1 )
        {

             nr++;
        }
    printf("%d", nr);
    return 0;
}