#include <iostream>
#include <string>
using namespace std;
string get_common_prefix(string s1, string s2) {
int len = min(s1.length(), s2.length());
string prefix = "";
for (int i = 0; i < len; i++) {
if (s1[i] == s2[i]) {
prefix += s1[i];
} else {
break;
}
}
return prefix;
}
void find_prefix() {
string productions[6] = {"x", "xy", "c", "a", "b", "ab"};
string prefix = productions[0];
for (int i = 1; i < 6; i++) {
prefix = get_common_prefix(prefix, productions[i]);
if (prefix == "") {
break;
}
}
if (prefix != "") {
cout << "The CFG contains the same prefix: " << prefix << endl;
} else {
cout << "The CFG does not contain the same prefix." << endl;
}
}
int main() {
find_prefix();
return 0;
}