#include <fstream>
using namespace std;

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

char ciur[2000001];

int main(){
    int i, j, n, nr = 0;
    fin >> n;
    for (i = 2;i <= n;i++)
        if (ciur[i] == 0){
            nr++;
            for (j = i*i;j <= n;j += i)
                ciur[j] = 1;
    }
    fout << nr;
    return 0;
}