MLE 0pts求助

#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=25,inf=1e18;
struct Node{
	string a,b;
	bool operator <(const Node &u)const{
		return b>u.b;
	}
}s[N];
int n,maxn=-inf;
signed main(){
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	cin>>n;
	for (int i=1;i<=n;i++){
		cin>>s[i].a;
		s[i].b=s[i].a;
		if (s[i].a.length()>maxn)maxn=s[i].a.length();
	}
	for (int i=1;i<=n;i++){
		while(s[i].b.length()<maxn){
			char c=s[i].b[s[i].b.length()-1];
			s[i].b.push_back(c);
		}
	}
	sort(s+1,s+n+1);
	for (int i=1;i<=n;i++){
		cout<<s[i].a;
	}
}