#include <fstream>

using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int n;
int v[2000005];
int i,j,nrprime;

int main()
{
    cin>>n;
    v[1]=1;
    for(i=2;i<=n;i++)
        if(v[i]==0)
        {
            nrprime++;
            for(j=i+i;j<=n;j+=i)
                v[j]=1;
        }
    cout<< nrprime << '\n';
    return 0;
}