#include <fstream>
#include <bitset>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset <2000003> v;
int main()
{
     int sol=0,i,j,N;
    fin>>N;
    for(i=3;i*i<N;i+=2)
    {
        if(!v[i])
        {
            for(j=i*i;j<N;j+=i)
            {
                v[j]=1;
            }
        }
    }
    for(i=3;i<=N;i+=2)
    {
        if(!v[i])
        {
            sol++;
        }
    }
    fout<<sol;
}