#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream o("ciur.out");
int main()
{

    int n;
    f >> n;
    int ciur[n+1];
    ciur[0] = 0;
    ciur[1] = 0;
    ciur[2] = 1;
    for (int i = 2; i <= n; i++)
    {
        if (ciur[i] == 0)
            continue;
        ciur[i] = 1;
        for (int j = i + i; j <= n; j += i)
        {
            ciur[j] = 0;
        }
    }

    int c = 0;
    for (int i = 2; i <= n; i++)
        if (ciur[i])
            c++;
    o << c;
}