#include <bits/stdc++.h>
using namespace std;
int n, i, j, nr;
bitset <2000001> w;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    for(i = 2; i <= n; i ++)
        if(w[i] == false)
        {
            nr ++;
            for(j = i * i; j <= n; j += i)
                w[j] = true;
        }
    g << nr;
    f.close();
    g.close();
    return 0;
}