#include <algorithm>
#include <complex>
#include <cstdlib>
#include <ctime>
#include <time.h>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <numeric>
#include <limits>
#include <type_traits>


using namespace std;
#define SAY_YES cout << "YES" << endl;
#define SAY_Yes cout << "Yes" << endl;
#define SAY_NO cout << "NO" << endl;
#define SAY_No cout << "No" << endl;
#define IFYES(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "YES" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "NO" << endl;  \
    }
#define IFYes(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "Yes" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "No" << endl;  \
    }
#define IFyes(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "yes" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "no" << endl;  \
    }
#define DEBUG_OUTPUT_ARRAY(XXX, ONE)                            \
    for (int i = 0; i < (ONE); i++)                             \
    {                                                           \
        cout << "DEBUG: i = " << i << " -> " << XXX[i] << endl; \
    }
#define DEBUG_OUTPUT_ARRAY2(XXX, ONE, TWO)                             \
    for (int i = 0; i < (ONE); i++)                                    \
    {                                                                  \
        cout << "<<< i = " << i << " >>>" << endl;                     \
        for (int j = 0; j < (TWO); j++)                                \
        {                                                              \
            cout << "DEBUG: j = " << j << " -> " << XXX[i][j] << endl; \
        }                                                              \
    }
#define DEBUG_OUTPUT_ARRAY2_BOX(XXX, ONE, TWO) \
    for (int i = 0; i < (ONE); i++)            \
    {                                          \
        cout << i << "  ";                     \
        for (int j = 0; j < (TWO); j++)        \
        {                                      \
            cout << XXX[i][j] << " ";          \
        }                                      \
        cout << endl;                          \
    }

typedef pair<long long int, long long int> pll;


const long long int mod = 1000000007;
const long long int INF = 1e18;
const long double PI=3.14159265358979323; 

long long int N,M,K,A,C,B,res=0,L[2005]={},Lsum[4005]={};
string S1,S2,S3;

int main()
{
    cout << fixed << setprecision(18);
    cin>>S1>>S2>>S3;
    long long int tmp=1;
    while(1){
        if(tmp==1){
            if(S1.size()==0){cout<<"A"<<endl;return 0;}
            if(S1[0]=='a'){
                tmp=1;
            }else if(S1[0]=='b'){
                tmp=2;
            }else{
                tmp=3;
            }
            S1=S1.substr(1,S1.size()-1);
        }else if(tmp==2){
            if(S2.size()==0){cout<<"B"<<endl;return 0;}
            if(S2[0]=='a'){
                tmp=1;
            }else if(S2[0]=='b'){
                tmp=2;
            }else{
                tmp=3;
            }
            S2=S2.substr(1,S2.size()-1);
        }else{
            
            if(S3.size()==0){cout<<"C"<<endl;return 0;}
            if(S3[0]=='a'){
                tmp=1;
            }else if(S3[0]=='b'){
                tmp=2;
            }else{
                tmp=3;
            }
            S3=S3.substr(1,S3.size()-1);
        }
    }
}    


Measured memory_bytes: 256