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

int main() {
    char s[101];
    scanf("%s", s);
    for (int i=0;s[i]&&s[i+1]; i += 2) {
        int num = (s[i]-'0')*10+(s[i+1]-'0');
        if (!isalpha((char)num)) {
            printf("Invalid Input\n");
            return 0;
        }
        printf("%c", num);
    }
    printf("\n");
    return 0:
}