#include <fstream>

using namespace std;

int n, x, i, j, d, sol, maxim;

bool f[2000001];

int main () {
    ifstream fin ("ciur.in");
    ofstream fout("ciur.out");
    fin >> n;
    for (i=2; i<=n; i++)
        if (f[i] == 0){
            sol++;
        	for (j=2*i; j<=n; j+=i)
        		f[j] = 1;
        }
    fout << sol;
    return 0;
}