#include <fstream>
#include <iostream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool v[2000001];
int main()
{
    int i, n, j, c = 0;
    fin >> n;
    for (i = 2; i * i <= n; i++)
    {
        if (v[i] == 1)
            continue;
        for (j = i * i; j <= n; j += i)
            v[j] = 1;
    }
    for (i = 2; i <= n; i++)
        if (v[i] == 0)
            c++;
    fout << c;
    return 0;
}