#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;
bitset <2000005> b;
int i,k,i1,n;
int main(void)
{
    FILE * f;
    f=fopen("ciur.in","r");
    ofstream g("ciur.out");
    fscanf(f,"%d",&n);
    k=0;
    for (i=2;i<=n;i++)
        if (b[i]==0)
        {
            k++;
            for (i1=i*i;i1<=n;i1=i1+i)
                b[i1]=1;
        }
    g<<k<<'\n';
    g.close();
    return 0;
}