#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
long long n,i,j,sol;
short f[2000020];
int main () {
    fin>>n;
    for (i=2;i<=n;i++) {
        if (f[i]==0) {
            sol++;
            for (j=i*i;j<=n;j+=i)
                f[j]=1;
        }
    }
    fout<<sol;
}