#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

bool prim[2000005];
int N,i,nr;
int main()
{
    fin>>N;
    for(i=2;i<=N;++i)
        if(prim[i]==false)
            {
                nr++;
                for(unsigned int j = i*i; j <= N; j = j + i)
                    prim[j] = true;
            }
    fout<<nr;
    return 0;
}