#include <iostream>
#include <fstream>

using namespace std;

const int VM = 2000001;
bool c[VM];

ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    int n, nr=0, i, j;
    in >> n;

    for(i=2; i*i<VM; i++)
        if(!c[i]){
            for(j=i*i; j<VM; j+=i)
                c[j]=true;
        }

    for(i=2; i<n; i++)
        if(!c[i])
            nr++;

    out << nr;

    return 0;
}