import java.util.Scanner;

public class Main{
  public static void main(String args[]){
    Scanner scan = new Scanner(System.in);
    String alpbt = scan.next();
    String[] list = {"a","b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n",
    		"o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"};
    int  i = 0;
    String result = null;
    while(!(list[i].equals(alpbt))){
    	i++;
    };
   	if(list[i].equals(alpbt)) {
   		result = list[i+1];
   	}
    System.out.println(result);
  }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz