#include <fstream>

using namespace std;
int n;
bool viz[2000005];
void citire()
{
    ifstream fin ("ciur.in");
    fin>>n;
    fin.close();
}
void rezolvare()
{
    int i,p,nrprime=0;
    ofstream fout ("ciur.out");
    viz[1]=1;
    for (i=4;i<=n;i+=2)
		viz[i]=1;
    for (i=3;i*i<=n;i=i+2)
        if (viz[i]==0)
        	for (int j = i * i; j <= n; j = j + 2*i)
			viz[j] = 1;
    nrprime = 1;
    for (i=3;i<=n;i+=2)
        if (viz[i]==0)
            nrprime++;
    fout<<nrprime;
    fout<<'\n';
    fout.close();
}
int main()
{
    citire();
    rezolvare();
    return 0;
}