#include <fstream>

using namespace std;
char ciur[2000005];

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");

    int N, i, j, nr = 0;
    fin >> N;

    for (i = 2; i <= N; i++){
        if (!(ciur[i])){
            nr++;
            for (j = i*i; j <= N; j += i){
                ciur[j] = 1;
            }
        }
    }
    fout << nr;
    return 0;
}