#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
long long j;
int n,i,f[2000005],pas;
int main () {
    fin>>n;
    pas=0;
    for (i=2;i<=n;i++) {
        if (f[i]==0) {
            pas++;
            for (j=i*i;j<=n;j+=i) {
                f[j]=1;
            }
        }
    }

    fout<<pas;
    return 0;
}