C++ :

#include <bits/stdc++.h>
using namespace std;
bool compare(int a,int b){
	return a > b;
}

int main(){
	int r[4010],i,n,k = 0,x;
	cin>>n;
	for(i = 0;i < n;i++){
		cin>>x;
		while(x != 0){
			r[k] = x % 10;
			x = x / 10;
			k++;
		}
	}	
	
	sort(r,r+k,compare);
	for(i = 0;i < k;i++){
		cout<<r[i];
	}
	
}

Python :

n=int(input())
a=input().split()
a=list(map(int,a))
b=[]
for i in a:
    k=len(str(i))
    for j in range(k):
        m=int(str(i)[j:j+1])
        b.append(m)
b=sorted(b)
b.reverse()
s=0
for i in range(0,len(b)):
    s=s*10+b[i]
print(s)