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

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

    scanf("%d",&x);

    printf("%d",Eratos(x));
}