#include <bits/stdc++.h>

using namespace std;

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

bitset <2000010>c;
int n, nr, i, j;

int main ()
{
    fin >> n;
    nr = 0;
    c[1] = 1;
    for (i=2; i<=n; i++)
    {
        if(c[i] == 0)
        {
            nr++;
            for(j=2*i; j<=n; j+=i)
                c[j]=1;
        }
    }
    fout << nr;
}