#include <fstream>
#include <bitset>
#define dim 2000010
using namespace std;
bool a[dim];
int i,j,n,nr;

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