#include <stdio.h>
#include <string.h>
int main() {
    int n;
    char s[101];
    scanf("%d", &s);
    
    int len = strlen (s);
    for (int i=0;i<len;i+=2) {
        int val =(s[i]-'0' *10 + (s[i+1]-'0'));
        
        if(( val >= 65 && val <= 90 || (val >= 97 && val <= 122))) {
            printf("Invalid input");
            return 0;
        }
        printf("%c", val);
    }
    return 0;
}