#include<fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n,i,j,sol;
char v[2000001];
int main ()
{
    fin>>n;
    for(i=2;i<=n;++i)
        if(v[i]==0){
            sol++;
            for(j=i+i;j<=n;j+=i);
        }
    fout<<sol;
    return 0;
}