codeforces 1092B

#include<bits/stdc++.h>
using namespace std;
int main()
{
          int n,i,x,c=0;
          cin>>n;
          vector<int>v;
          for(i=0;i<n;i++){
                    cin>>x;
                    v.push_back(x);
          }
          sort(v.begin(),v.end());
          for(i=0;i<n;i=i+2){
                    if(v[i]!=v[i+1]){
                              c+=(max(v[i],v[i+1])-min(v[i],v[i+1]));
                    }
          }
          cout<<c<<endl;


}