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

using ld=long double;

signed main(){
  int n;cin>>n;
  vector<ld> v(n);
  for(int i=0;i<n;i++)cin>>v[i];
  sort(v.begin(),v.end());
  ld ans1=0,ans2=0;
  for(int i=0;i<n&&v[i]<0;i++)ans1+=v[i];
  for(int i=n-1;i>=0&&v[i]>0;i--)ans1+=v[i];
  cout<<fixed<<setprecision(10)<<ans1+ans2<<endl;
}