#include <iostream>
#include<fstream>
#include<string.h>

using namespace std;

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n;
    f >> n;

    int c = 0;
    int a[n];
    memset(a, 0, sizeof(a));

    for (int i = 2; i <= n; i++) {
        if (a[i] == 0) {
            c += 1;
            for (int j = i+1; j <= n; j++) {
                if (j%i==0) a[j]=1;
            }
        }
    }
    g << c;
    f.close();
    g.close();

    return 0;
}