#include <iostream>
#include <fstream>

using namespace std;
int a[2000010];
int main()
{
    int n,i,j,k=-1;
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    fin>>n;
    for (i = 2; i <= n;i++)
        a[i] = 1;
    for (i = 2;i <= n;i++)
        if (a[i])
        {
            k++;
            for (j = j*2;j <= n;j += i)
                a[j] = 0;
        }
    fout<<k;
    return 0;
}