#include <stdio.h>
#define Nmax 2000001
using namespace std;
bool a[Nmax];
int Eratos(int n)
{
    int nr=0;
    for(int i=2;i<=n;i++)
        if(!a[i])
        {
           nr++;

        for(int j=2;j*i<=n;j++)
            a[i*j]=1;
        }
    return nr;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    int n;

    scanf("%d",&n);
    printf("%d",Eratos(n));
}