#include <fstream>

using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

bool f[2000010];
int n,i,j,prime;

int main () {

    fin>>n;
    for (i=2;i<=n;i++) {
        if (f[i]==0) {
            prime++;
            for (j=i+i;j<=n;j+=i)
                f[j]=1;
        }
    }
    fout<<prime<<"\n";


    return 0;
}