#include <fstream>
using namespace std;
ifstream cin("segredo.in");
ofstream cout("segredo.out");

char c;  //a=97 z=122
int a[125],minA,maxA=0;

int main(){
    while(cin>>c)
    {
        cin>>c;
        a[(int)c]++;
    }
    minA=a[97];
    for (int i=97;i<123;i++)
    {
        if(minA>=a[i]) minA=a[i];
        if(maxA<=a[i]) maxA=a[i];
    }
    for (int i=97;i<123;i++)
    {
        if(a[i]==maxA) cout<<(char)i;
    }
    cout<<endl;
    for (int i=97;i<123;i++)
    {
        if(a[i]==minA) cout<<(char)i;
    }

    return 0;
}