#include <fstream>
#include <cmath>
using namespace std;
int n, i, j, p[2000], ciur[2000], c;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

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