#include <iostream>

#include <vector>

using namespace std;

#define REP(i,n) for(int i=0;i<(n);++i)

#define FOR(i,a,b) for(int i=(a);i<=(b);++i)

#define RFOR(i,a,b) for(int i=(a);i>=(b);--i)

class Solution {

string longestCommonPrefix(vector<string> &strs) {

if (strs.empty()) return "";

REP(i,strs[0].length()) {

FOR(j,1,strs.size()-1) {

if (i >= strs[j].length() || strs[0][i] != strs[j][i]) return strs[0].substr(0, i);

}

}

return strs[0];

}

};

int main() {

vector<string> mm;

mm.push_back("abc");

mm.push_back("abd");

mm.push_back("aaa");

Solution s = Solution();

cout << s.longestCommonPrefix(mm) << endl;

return 0;

}