#include <fstream>

using namespace std;

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

bool a[2000001];

int main()
{
    int nr, n, i, j;
    nr = 0;
    in>>n;
    for ( i = 2; i <= n; i++ )
        a[i]=1;
    for ( i = 2; i * i <= n; i++ )
        if ( a[i] )
            for ( j = i; j <= n / i; j++ )
                a[i * j] = 0;
    for ( i = 2; i <= n; i++ )
        if ( a[i] )
            nr++;
    out<<nr;
    return 0;
}