#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool p[2000010];
int N,nr;
int main()
{
    f >> N;
    nr = 1;
    for(int i = 3; i <= N; i += 2){
        if(p[i] == 0){
            nr++;
            for(int j = i + i + i; j <= N; j = j + 2*i){
                p[j] = 1;
            }
        }
    }
    g << nr;
    ///110  110000
    ///29  10453
    return 0;
}