#include<stdio.h>
#include<string.h>
int main()
{
    char str[100];
    scanf("%s", st);
    int len = strlen(str);
    for(int i = 0; i < len; i+=2)
    {
        int value1 = str[i]-'0';
        int value2 = str[i+1]-'0';
        int value = value1 * 10 + value2;
        if(value < 65 || value > 122 || value == 96)
        {
            printf("Invalid Input\n");
            return 0;
        }
        printf("%c", value);
    }
    return 0;
}