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

void solve(){
    int n;
    cin>>n;
    
    map<int, int>mp;
    int ans = 0;
    for(int i = 0; i < n; i++){
    	int x;
    	cin>>x;
    	mp[x] = i;
    	ans ^= x;
    }
    cout<<mp[ans]<<"\n";
}

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int test = 1;
    // cin>>test;
    while(test--)
        solve();
}