#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
int N,i,j,v[2000000],k;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f>>N;
    k=1;
    for(i=3; i<=N; i=i+2)
    {
        if(v[i]==0)
        {
            for(j=2*i; j<=N; j=j+i)
                v[j]=1;
            k++;
        }

    }
    g<<k;
    return 0;
}