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