Help me in solving ZCO13001 problem

help
,
1

My issue

//TLE in last 2 cases

My code

#include <bits/stdc++.h>
using namespace std;

int main() {
	// your code goes here
	long long n;
	cin>>n;
	long long a[n],m=0,k;
	for(int i=0;i<n;i++)cin>>a[i];
	for(int i=0;i<n;i++){
	    for(int j=i+1;j<n;j++){
	        k=abs(a[i]-a[j]);
	        m=m+k;
	    }
	}
	cout<<m;
	return 0;
}

Problem Link: CodeChef: Practical coding for everyone