PAT A1038 recover the smallest number (30)

#include<cstdio>
#include<algorithm>
#include<string>
#include<cstring>
#include<iostream>
using namespace std;
bool cmp(string a,string b){
return (a+b)<(b+a);
}
int main(){
string str[10010];
int n,i;
cin>>n;
for(i=0;i<n;i++){
cin>>str[i];
}
sort(str,str+n,cmp);
i=0;
while(str[i][0]=='0'){
str[i].erase(0,1);
if(str[i].size()==0){
i++;
n--;
}
}
if(n==0) printf("0");
for(i=0;i<n;i++){
cout<<str[i];
}
system("pause");
return 0;


}