#include <fstream>

using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
bool x[2000001];
int n, i, k,nr;
int main()
{
    cin>>n;
    for(i=2;i<=n;i++)
        x[i]=1;
    for(i=2;i*i<=n;i++)
        if(x[i])
        {
            nr++;
            for(k=i*i;k<=n;k+=i)
                x[k]=0;
        }
    cout<<nr;
    cin.close();
    cout.close();
    return 0;
}