#include <fstream>

using namespace std;

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

bool f[2000001];
int cnt;

int main()
{
    int n;
    fin>>n;
    for ( int i = 2; i <= n; ++i )
        if ( f[i] == 0 )
            for ( int j = 2*i; j <= n; j += i )
                f[j] = 1;
    for ( int i = 2; i <= n; ++i )
        if ( f[i] == 0 )
            cnt++;
    fout<<cnt;
}