#include <iostream>
#include <fstream>

using namespace std;
int N, k, prim[2000005];
int main()
{
    int i, j
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in >> N;
    
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++k;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }
    out << k;
}