#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset <2000001> v;
int main()
{
    int nr = 1,n;
    in >> n;
    for(int i = 3 ; i*i <= n ; i +=2)
        if(v[i] == 0)
        for(int j = i*i ; j <= n ; j +=2*i)
            v[j] = 1;
    for(int i = 3 ; i <= n ; i +=2)
        if(v[i] == 0)
            nr++;
    out<<nr;
    return 0;
}