#include<>
#include<>
#include<>
#include<>

int main()
{
    char in[101];
    fegts(in,101,stdin);
    in[strcpn(in," ")] = 0;
    int len = strlen(in);
    if(len %2!=0)
    {
        printf("Invalid input");
        return 0;
    }
    for(int i =0; i<len; ++i)
    { if(!isdigit(in[i]))
    {  printf("Invalid input");
        return 0;
    } }
    char o[51];
    for(int i =0; i<len; i+=2)
    {
        int num = (in[i]-'0')*10 + (in[i+1]-'0');
        if(num<65|| num>90)
        {
            printf("Invalid input");
        return 0;
        }
        printf("%c",num);
    }
    printf(" ");
    return 0;
}