#include <fstream>
#define NMax 2000005
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int N,Sol;
bool prim[NMax];

int main()
{
    fin>>N;
    for(int i = 2;i<=N; i++)
        {
            if(prim[i]==0)
                {
                    Sol++;
                    for(int j = i+i; j<=N; j = j + i)
                        prim[j]=1;
                }
        }
    fout<<Sol;
    return 0;
}