#include <iostream>
#include <fstream>

using namespace std;

int n, contuar = 0;
char v[2000005];
ifstream ciurin("ciur.in");
ofstream ciurout("ciur.out");

int main()
{
    ciurin >> n;

    for(int i = 2; i <= n; i++)
    {
        if(v[i] == 0)
        {
            contuar++;
            for(int d = i * i; d <= n; d = d + i)
            {
                v[d] = 1;
            }
        }

    }

    ciurout << contuar;

    ciurin.close();
    ciurout.close();

    return 0;
}