#include <iostream> // cout, endl, cin
#include <string> // string, to_string, stoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <cstdint> // int64_t, int*_t
#include <cstdio> // printf
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set
#include <stack> // stack
#include <deque> // deque
#include <unordered_map> // unordered_map
#include <unordered_set> // unordered_set
#include <bitset> // bitset
#include <cctype> // isupper, islower, isdigit, toupper, tolower
#include <math.h>
#include <cmath>
using namespace std;

#define int long long
#define endl "\n"
#define all(v)  v.begin(),v.end()
#define fir first
#define sec second
#define m_p make_pair
#define rep(i,n)  for(int i=0; i<(int) (n); i++)
#define vecin(v) for(int i=0; i<(int)v.size(); i++)cin>>v[i];
#define vecout(v,n) for(int i=0; i<n; i++)cout<<v[i]<<" "; cout<<endl;

const int mod = 1000000007;
const int INF = 2000000015;
const int MAX = 510000;
const int MOD = 1000000007;
long long fac[MAX], finv[MAX], inv[MAX];
int jousu(int x00, int y00) {
	int z00 = 1;
	for (int i = 0; i < y00; i++) {
		z00 *= x00;
	}
	return z00;
}
int keta(int x00) {
	int z00 = x00;
	int w00 = 0;
	while (z00 != 0) {
		z00 /= 10;
		w00++;
	}
	return w00;
}
int krag(double xx) {
	return INF - (int)(INF - xx);
}

//x未満の要素数を返す二分探索関数
int b_s(vector<int>&vecxx, int xx) {
	if (xx <= vecxx[0]) { //x以下の要素数を返させる時は"<"に変える
		return 0;
	}
	if (vecxx.back() < xx) { //x以下の要素数を返させる時は"<="に変える
		return vecxx.size();
	}
	int aa1 = 0, aa2 = vecxx.size() - 1, aa3;
	while (aa1 + 1 < aa2) {
		aa3 = (aa1 + aa2) / 2;
		if (vecxx[aa3] >= xx) { //x以下の要素数を返させる時は">"に変える
			aa2 = aa3;
		}
		else {
			aa1 = aa3;
		}
	}
	return aa2;
}


int modinv(int a, int m) {
	int b = m, u = 1, v = 0;
	while (b) {
		int t = a / b;
		a -= t * b; swap(a, b);
		u -= t * v; swap(u, v);
	}
	u %= m;
	if (u < 0) u += m;
	return u;
}
int modpow(int a, int n) {
	int res = 1;
	while (n > 0) {
		if (n & 1) res = res * a % mod;
		a = a * a % mod;
		n >>= 1;
	}
	return res;
}
//n個を1個以上のx組のグループに分ける重複組み合わせはcom(n-1,x-1)
//グループが0個でもいいときはnにxを足す

int com(int xx, int yy) {
	int zz = 1;
	for (int i = xx; i > xx - yy; i--) {
		zz *= i;
		zz %= mod;
	}
	for (int i = 1; i <= yy; i++) {
		zz *= modinv(i, mod);
		zz %= mod;
	}
	return zz;
}
int gcd(int xx, int yy) {
	int p = xx;
	int q = yy;
	if (q > p)swap(p, q);
	while (p % q != 0) {
		p %= q;
		swap(p, q);
	}
	return q;
}
int lcm(int xx, int yy) {
	return xx * yy / gcd(xx, yy);
}
bool prime(int xx) {
	int a = xx;
	for (int i = 2; i * i <= xx; i++) {
		if (xx % i == 0) {
			return 0;
		}
	}
	return 1;
}



signed main() {
	string s;
	char c = 'a';
	vector<char>vec1,vec2,vec3;
	cin >> s;
	for (int i = s.size() - 1; i >= 0; i--) {
		vec1.push_back(s[i]);
	}
	cin >> s;
	for (int i = s.size() - 1; i >= 0; i--) {
		vec2.push_back(s[i]);
	}
	cin >> s;
	for (int i = s.size() - 1; i >= 0; i--) {
		vec3.push_back(s[i]);
	}
	while (1) {
		if (c == 'a') {
			if (vec1.size() == 0) {
				cout << "A" << endl;
				return 0;
			}
			c = vec1.back();
			vec1.pop_back();
		}
		else if (c == 'b') {
			if (vec2.size() == 0) {
				cout << "B" << endl;
				return 0;
			}
			c = vec2.back();
			vec2.pop_back();
		}
		else if (c == 'c') {
			if (vec3.size() == 0) {
				cout << "C" << endl;
				return 0;
			}
			c = vec3.back();
			vec3.pop_back();
		}
	}
	if (vec1.size() == -1) {
		cout << "A" << endl;
	}
	if (vec2.size() == -1) {
		cout << "B" << endl;
	}
	if (vec3.size() == -1) {
		cout << "C" << endl;
	}
}




Measured memory_bytes: 256