java Uva1644.java

Posted 2021-05-08

import java.util.*;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner scanner = new Scanner(System.in);
		boolean primeTable[] = new boolean[1299710];
		for(int i=0;i<primeTable.length;i++){
			primeTable[i] = true;
		}
		primeTable[0] = primeTable[1] = false;
		for(int i=2;i<primeTable.length;i++){
			if(primeTable[i]){
				for(int j=i+i;j<primeTable.length;j+=i){
					primeTable[j] = false;
				}
			}
		}
		
		while(scanner.hasNext()){
			int num = scanner.nextInt();
			if(num == 0 ){
				break;
			}
			int end = 0,head = 0;
			for(int i=num;i<primeTable.length;i++){
				if(primeTable[i]){
					end = i;
					break;
				}
			}
			for(int i=num;i>0;i--){
				if(primeTable[i]){
					head = i;
					break;
				}
			}
			
			System.out.println(end-head);
		}
	}

}