#include <fstream>
#include <cmath>
using namespace std;
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n;
    int i,gogu=0,j;
    bool v[2000001];
    in>>n;
    for(i=2;i<=n;i++)
        if(v[i]==0)
        {
            for(j=i+i;j<=n;j=j+i)
                v[j]=1;
        gogu++;
        }

    out<<gogu;
    in.close();
    out.close();
    return 0;
}