#include <iostream>
#include <cstdio>
using namespace std;

char c[2000005];
int n;

int ciur()
{
    int nr=0;
    c[0]=c[1]=1;
    for (int i=2; i<=n; i++)
         if (c[i] == 0)
             {
                 nr++;
                 for (int j=2*i; j<=n; j+=i)
                    c[j]=1;
             }
    return nr;
}

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

    scanf("%d",&n);
    printf("%d",ciur());

    return 0;
}