#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bitset<2000000> ciur;
int main() {
    int n, cnt = 0;
    in>>n;
    for (int i = 4; i <= n; i += 2)
        ciur[i] = true;
    if (n == 1){
        out<<"0\n";
        return 0;
    }
    if (n == 2){
        out<<"1\n";
        return 0;
    }
    cnt = 1;
    for (int i = 3; i <= n; i += 2) {
        if (!ciur[i]) {
            cnt++;
            for (int j = i * i; j <= n; j += i) {
                ciur[j] = true;
            }
        }
    }
    out<<cnt<<"\n";
    return 0;
}