#include <iostream>
#include <fstream>

using namespace std;
int a[1000000];
int main()
{
    int n,i,j,count=1;
    ifstream fin("ciur.in");
    fin>>n;
    fin.close();
    for(i=3;i<=n;i+=2)
            if(a[i]==0)
                {
                    count++;
                    for(j=i*i;j<=n;j+=2*i)
                        a[j]=1;
                }

    ofstream fout("ciur.out");
    fout<<count<<"\n";
    fout.close();
    return 0;
}