#include <iostream>
#include <fstream>
#include <bitset>
#define NUM 2000005
using namespace std;
bitset<NUM> ciur;
int n, total;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    for(int i = 2; i <= n; ++i)
    {
        if(!ciur[i])
        {
            total++;
            for(int d = i * i; d <= n; d += i)
                ciur[d] = 1;
        }
    }
    g << total;
    f.close();
    g.close();
}