#include <fstream>
#define MAX 2000001

using namespace std;

int n;
bool p[MAX];

int main()
{
    int i, j, rez = 0;
    ifstream fin("ciur.in");
    fin >> n;
    fin.close();
    
    memset(p, 1, sizeof(p));
    
    for (i = 2; i <= n; i++)    
        if (p[i])
        {
            rez++;
            for (j = i+i; j <= n; j += i)
                p[j] = 0;
        }
    
    ofstream fout("ciur.out");
    fout << rez << "\n";
    fout.close();
    
    return 0;    
}