#include <cstdio>
using namespace std;

int n, nr, i, j;
bool viz[2000100];
int main ()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    scanf("%d", &n);
    nr=0;
    for (i=2; i<=n; i++){
        if (viz[i]==0){
            nr++;
            for (j=2; j*i<=n; j++)
                viz[i*j]=1;
        }
    }
    printf("%d", nr);
    return 0;
}