#include <fstream>
using namespace std;
char v[2000002];
int main()
{
    int n,i,j,sol;
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    in>>n;
    sol=0;
    for(i=2;i<=n;i+=1)
    {
        if(v[i]==0)
        {
            sol++;
            for(j=i*2;j<=n;j+=i)
            {
                v[j]=1;
            }
        }
    }
    out<<sol;
    return 0;
}