#include <iostream>
#include <fstream>
#define NMAX 2000005
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool ciur[NMAX];
int getPrimesNumber(int N) {
    for (int i = 2; i <= N; ++i) {
        if (ciur[i] == false) {
            if (long(i) * i <= N) {
                for (int j = i * i; j <= N; j += i) {
                    ciur[j] = true;
                }
            }
        }
    }
    int con = 0;
    for (int i = 2; i <= N; ++i) {
        if (!ciur[i]) {
            ++con;
        }
    }
    return con;
}
int main()
{
    int n;
    fin >> n;
    fout << getPrimesNumber(n);
    return 0;
}