#include <iostream>
#include <fstream>
using namespace std;
#define NMax 2000005


ifstream fin("ciur.in");
ofstream fout("ciur.out");
int prim[NMax], n;
int main()
{
    int contor = 0;
    fin >> n;
    for(int i = 2; i <= n; i++)
    {
        prim[i] = 1;
    }
    for(int i = 2; i <= n; i++)
    {
        if(prim[i])
        {
            contor++;
            for(int j = i + i; j <= n; j += i)
                prim[j] = 0;
        }
    }
    fout << contor;
}