#include<stdio.h>
#include<ctype.h>
void reverse(char s[], int i) {
    if (s[i] == '\0') return;
    reverse(s, i + 1);
    putchar(s[i]);
}
int main() {
    char s[101];
    fgets(s, 101, stdin);
    for (int i = 0; s[i]; i++)
         if (isdigit(s[i])) {
             printf("Invalid input");
             return 0;
         }
    reverse(s, 0);
    return o;
}