#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
typedef long long ll;
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> pbds;
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#define ios ios_base::sync_with_stdio(0) ; cin.tie(0) ; cout.tie(0)
#define so sizeof
#define pb push_back
#define cl clear() ;
#define vl vector<ll>
#define sz size()
#define len length()
#define el endl;cout.flush()
#define be begin()
#define fi first
#define se second
#define br break
#define en end()
#define ro return 0
#define br break
#define eb emplace_back
#define con continue
#define ms(x) memset(x , 0, so x)
#define all(x) (x).be , (x).en
#define acc(x) accumulate((x).be , (x).en , 0ll)
#define forn(i,a,b) for(ll i=a;i<=b;++i)
#define rng_58 mt19937 rng(chrono::steady_clock::now().time_since_epoch().count())
#define vll vector<pair<ll,ll> >
#define pll pair<ll,ll>
#define plll pair<ll,pair<ll,ll>>
#define plvl pair<pair<ll,ll> ,ll>
#define mp make_pair
#define trace3(a,b,c) cerr <<"a is " << a << " b is " << b << " c is " << c << el;
#define trace4(a,b,c,d) cerr <<"a is " << a << " b is " << b << " c is " << c <<" d is " << d << el ;
#define trace5(a,b,c,d,e) cerr <<"a is " << a << " b is " << b << " c is " << c <<" d is " << d << " e is " << e << el;
#define trace6(a,b,c,d,e,f) cerr <<"a is " << a << " b is " << b << " c is " << c <<" d is " << d << " e is " << e << " f is " << f << el ;

int main()
{
    ios;
    string s1 , s2 , s3 ;
    cin >> s1 >> s2 >> s3 ;
    reverse(all(s1));
    reverse(all(s2));
    reverse(all(s3));
    stack<char> a , b , c;
    for(auto &x :s1 ) {
        a.push(x);
    }
    for(auto  &x : s2) {
        b.push(x);
    }
    for(auto &x : s3) {
        c.push(x) ;
    }
    ll winner = -1 ;
    ll turn = 1 ;
    while(1) {
        if(turn == 1){
            if(a.empty() == true){
                winner = 1 ;
                br ;
            }
            else {
                char ch  = a.top();
                a.pop();
                if(ch == 'a') turn = 1 ;
                else if(ch == 'b') turn = 2 ;
                else if(ch == 'c') turn = 3 ;
            }
        }
        else if(turn == 2 ){
           if(b.empty() == true){
                winner = 2 ;
                br ;
            }
            else {
                char ch  = b.top();
                b.pop();
                if(ch == 'a') turn = 1 ;
                else if(ch == 'b') turn = 2 ;
                else if(ch == 'c') turn = 3 ;
            }
        }
        else if(turn == 3){
            if(c.empty() == true){
                winner = 3 ;
                br ;
            }
            else {
                char ch  = c.top();
                c.pop();
                if(ch == 'a') turn = 1 ;
                else if(ch == 'b') turn = 2 ;
                else if(ch == 'c') turn = 3 ;
            }
        }
    }
    if(winner == 1 ) {
        cout << "A" << el ;
        ro ;
    }
    else if(winner == 2) {
        cout << "B" << el ;
    }
    else cout << "C" << el ;
    ro ;
}































Measured memory_bytes: 256