#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;
bool v[2000005];
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n;
    fin >> n;
    int i, j;
    for (i = 2; i <= n; i++)
        if (v[i] == 0)
        for (j = 2 * i; j <= n; j = j + i)
            v[j] = 1;
    int nr = 0;
    for (i = 2; i <= n; i++)
        if (v[i] == 0)
        nr++;
    fout << nr;
    return 0;
}