#include <iostream>
#include <fstream>

using namespace std;

bool v[2000001];

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n, i, s=0, j;
    fin>>n;

    for (i=2; i<n; i++)
    {
        if (v[i]==0)
        {
            s++;
            for (j=2*i; j<n; j=j+i)
                v[j]=1;
        }
    }

    fout<<s;
    return 0;
}