#include <iostream>
#include <math.h>
#include <fstream>
#define DIMMAX 2000000
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
long int nrprime[DIMMAX];
int main()
{
    int i, j, nr = 0, N;
    fin>>N;
    for (i = 1; i <= N; i++)
        nrprime[i] = 1;
    for (i = 2; i < sqrt(N); i++)
    {
        if (nrprime[i] == 1)
            for (j = 2 * i; j <= N; j += i)
                nrprime[j] = 0;
    }
    for (i = 2; i <= N; i++)
        if (nrprime[i] == 1)
            nr++;
    fout<<nr;
    fin.close();
    fout.close();
    return 0;
}