#include <cstdio>
#include <bitset>

#define NMAX 2000005

using namespace std;

int n,nr=1;

bitset <NMAX>ap;

int main()
{

    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    scanf("%d",&n);

    for (int i=3;i<=n;i+=2)
    if (!ap[i]){
        nr++;
        for (int j=i*i;j<=n;j+=i)ap[j]=1;
    }
    printf("%d",nr);

    fclose(stdin);
    fclose(stdout);
}