Bug in this code

#1

import java.util.*;
public class Main {
public static void main(String args[]) {
// Your Code Here
Scanner sc=new Scanner(System.in);
int diff,c=0;
String s=sc.nextLine();
StringBuilder sb=new StringBuilder(s);
for(int i=0;i<s.length()-1;++i){
diff=s.charAt(i+1)-s.charAt(i);
sb.insert(c+i+1,diff);
c++;
}

	System.out.print(sb);
}

}

can you pls find the bug where the test case 0 is faling?