#include <iostream>
#include <fstream>
using namespace std;
bool w[20001];
int n, cnt, i, j;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");

    f >> n;
    w[0] = w[1] = true;
    for(i = 2; i <= n; ++ i){
        if(w[i] == false){
            cnt ++;
            for(j = i + i; j <= n; j += i)
                w[j] = true;
        }
    }
    g << cnt;
    return 0;
}