#include<bits/stdc++.h>
using namespace std;
char a[1010]={0};
char b[1010]={0};
int main()
{
    freopen("troublekey.in","r",stdin);
    freopen("troublekey.out","w",stdout);
    int c,i,j;
    char ans;
    bool d;
    cin>>a>>b;
    ans='0';c=0;d=false;
    if(strlen(a)==strlen(b))
    {
        for(i=0;i<strlen(a);i++)
        {
            if(a[i]!=b[i])
            {
                cout<<a[i]<<" "<<b[i]<<endl;
                cout<<"-";
                break;
            }
        }
    }
    else
    {
        for(i=0;i<strlen(a);i++)
        {
            if(a[i]==ans)
            {
                c++;
            }
            else
            {
                if(i>=strlen(b)&&ans=='0')
                {
                    ans=a[i];
                    break;
                }
                if(a[i]!=b[i-c])
                {
                    for(j=i+1;;j++)
                    {
                        if(a[i]!=a[j])
                        {
                            if(a[j]==b[j-c]||ans!='0')
                            {
                                if(d==false)
                                {
                                    cout<<a[i]<<" "<<b[i-c]<<endl;
                                    d=true;
                                }
                            }
                            else
                            {
                                ans=a[i];
                                c++;
                            }
                            break;
                        }
                    }
                }
            }
            if(d==true&&ans!='0')
            {
                break;
            }
        }
        cout<<ans;
    }
    return 0;
}