#include <fstream>
#include <cmath>
using namespace std;
int n, i, j, c;
bool ciur[2000005];
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

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