#include <bits/stdc++.h>

using namespace std;
const int INF = 0x3f3f3f3f;

//两个字符串，最小重叠部分的长度
string merge(string a, string b) {
    int n = INF;
    //相连接 两层循环找出a的所有可能子串，然后与b串的前缀进行对比，找到最长的
    for (int i = a.size() - 1; i > 0; i--) {
        string t = a.substr(i);
        if (b.compare(0, t.size(), t) == 0) { //如果相等则输出为0，不等则输出为-1。
            n = a.size() - i;//长度
            break;
        }
    }
    if (n < INF) return a + b.substr(n);
    else return "";
}

int main() {
    string c = merge("beast", "astonish");
    cout << c << endl;

    c = merge("cheat", "tact");
    cout << c << endl;

    c = merge("cheat", "choose");
    cout << c << endl;

    c = merge("envelope", "envelope");
    cout << c << endl;

    c = merge("abababab", "abababc");
    cout << c << endl;

    c = merge("abababab", "abababab");
    cout << c << endl;

    return 0;
}