C++

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#include <bits/stdc++.h>

using namespace std;

using ll = long long;

ll gcd(ll a, ll b) {
	if (b == 0) return a;
	return gcd(b, a % b);
}

Java

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import java.io.*;
import java.util.*;

public class Prod1ModN {
	public static void main(String[] args) {
		Kattio io = new Kattio();
		int n = io.nextInt();

		ArrayList<Long> coprimes = new ArrayList<>();

Python

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import math

n = int(input())
coprimes = []

"""
This array stores all of the numbers
which are less than n and are coprime with n.
"""