#include<stdio.h>
int main(){
    int n;
    scanf("%d",&n);
    if(n<=0){
        printf("Invalid input");
        return 0;
    }
    int original=n;
    int reversed=0;
    while(n>0){
    int rem=n%10;
    reversed=reversed*10+rem;
    n=n/10;
    }
    if(original==n){
        printf("unchanged");
    }
    else{
        printf("%d",rem);
    }
    return 0;
}