#include <fstream>
#define IN "ciur.in"
#define OUT "ciur.out"
#define DMAX 2000008
using namespace std;
ifstream fin(IN);
ofstream fout(OUT);

int n, nb;
char v[DMAX];

int main(){
    fin >>n;

    int i, j;
    for (i = 2; i <=n; ++i)
        if (!v[i]){
            ++nb;
            for (j = i + i; j <= n; j+=i)
                v[j] = 1;
        }
    fout <<nb<<'\n';
    fout.close();
    return 0;
}