#include<stdio.h>
#include<string.h>
#include<ctype.h>
const char* mapping[]={
    "",
    "",
    "ABC",
    "DEF",
    "GHI",
    "JKL",
    "MNO",
    "PQRS",
    "TUV",
    "WXYZ",
};
void printcombinations(char* digits,int curr,char* result,int n,int* first){
    if(curr==n){
        if(*first){
            printf("[");
            *first=0;
        }else{
            printf("%s",result);
            return;
        }
        int digit=digits[curr]-'0';
        const char* letters=mapping[digit];
        for(int i=0;letters[i]!= '\0';i++){
            result[curr]=letters[i];
            printcombinations(digits,curr +1,result,n,first);
        }
    }
    int main(){
        char digits[101];
        scanf("%100s",digits);
        int n=strlen(digits);
        for(int i=0;i<n;i++0{
            if(!isdigit[i]||digits[i]<'2'||digits[i]>'9'){
                printf("Invalid input\n");
                return 0;
            }  
        }
        if(n==0){
            printf("[]\n");
            return 0;
        }
        }
    }
}