package MathPrograms;
import trick.FastReader;

public class greatestPrimeCheck {

	public static int greatestPrime(int num) {
		int calculatedPrimeNo = 0;
		if (num == 0 || num == 1) {
			return 2;
		}
		do {
			boolean isPrime = true;
			for (int i = 2; i < Math.sqrt(num); i++) {
				if (num % i == 0) {
					isPrime = false;
					break;
				}
			}
			if (isPrime) {
				calculatedPrimeNo = num;
			} else {
				num++;
			}
		} while (calculatedPrimeNo != num);
		return calculatedPrimeNo;
	}

	public static void main(String[] args) {
		FastReader fc=new FastReader();
		System.out.println("Enter the number: ");
		int num = fc.nextInt();
		System.out.println(greatestPrime(num) - num);
	}

}