C++ :

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
int c[1000001][2],s[100001],a[100001],ans;
int pw[21],n;
void add(int x,int y)
{
  while (x<=1000000)
    {
      c[x][y]++;
      x+=(x&(-x));
    }
}
int query(int x,int y)
{
  int sum=0;
  while (x)
    {
      sum+=c[x][y];
      x-=(x&(-x));
    }
  return sum;
}
int main()
{int i,j,flag,cnt;
  cin>>n;
  for (i=1;i<=n;i++)
    {
      scanf("%d",&s[i]);
      s[i]+=s[i-1];
    }
  pw[0]=1;
  for (i=1;i<=20;i++)
    pw[i]=pw[i-1]*2;
  for (i=0;i<=20;i++)
    if (pw[i]<=s[n])
      {
    memset(c,0,sizeof(c));
    flag=0;
    add(1,0);
    for (j=1;j<=n;j++)
      {
        int tmp=s[j]&pw[i];
        if (tmp) cnt=query(a[j]+1,0)+query(1000001,1)-query(a[j]+1,1);
        else cnt=query(a[j]+1,1)+query(1000001,0)-query(a[j]+1,0);
        if (cnt%2==1) flag^=1;
        add(a[j]+1,(bool)tmp);
        if (tmp) a[j]|=pw[i]; 
      }
    if (flag) ans|=(pw[i]);
      }
  cout<<ans;
}