#include <cstdio>

using namespace std;

int n,q=0,w[2000005];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d", &n);
    for (int i=2; i<=n; i++)
        w[i]=1;
    for (int i=2; i<=n; i++)
    {
        if (w[i])
        {
            ++q;
            for (int j=i+i; j<=n; j+=i)
                w[j]=0;
        }
    }
    printf("%d", q);
    fclose(stdin);
    fclose(stdout);
    return 0;
}