#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
const int maxn = 2000005;
bitset <maxn> prim;
int main()
{
    int n;
    in >> n;
    for(int i = 2; i <= n; i++)
        prim[i] = 1;
    for(int i = 2; i <= n; i++)
        if(prim[i] == 1)
            for(int j = i + i; j <= n; j = j + i)
                prim[j] = 0;
    int nr = 0;
    for(int i = 1; i <= n; i++)
        nr = nr + prim[i];
    out << nr << "\n";
    return 0;
}