#include<stdio.h>
#include<string.h>
#include<stdlib.h>

int main() {
    char input[ 101 ];
    scanf("%s", input);
    
    int len = strlen(input);
    
    if (len % 2 != 0) {
        printf("Invalid Input");
        return 0;
    }
    
    char result[51];
    
    int pos = 0;
    int invalid = 0;
    
    for (int i = 0; i < len; i += 2) {
        char pair [3];
        pair [0] = input[i];
        pair [1] = input[i + 1];
        pair [2] = '\0';
        
        int ascii = atoi(pair);
        
        if ((ascii >= 65 && ascii <= 90) || (ascii >= 97 && ascii <= 122)) {
            result[pos++] = (char)ascii;
        } else {
            valid = 1;
             break;
        }
    }
    
    result[pos] = '\0';
    
    if (invalid)
        printf("Invalid Input");
    else 
        printf("%s", result);
        
    return 0;
    
}