#include <fstream>
using namespace std;

//Constante
const int sz=(int)2e6-1;

//Variabile
FILE *in, *out;

bool notPrime[sz];
int n,answer=1;


int main()
{
    in=fopen("ciur.in","rt");
    out=fopen("ciur.out","wt");
    fscanf(in,"%d",&n);

    for(int i=3 ; i<=n ; i+=2)
    {
        if(!notPrime[i])
        {
            ++answer;
            for(int j=i+i ; j<=n ; j+=i)
                notPrime[j] = true;
        }
    }


    fprintf(out,"%d\n",answer);

    fclose(in);
    fclose(out);
    return 0;
}