Gauss Elimination for xor

//https://codeforces.com/contest/1101/problem/G

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

#define MAX 200005
#define ll long long

ll a[MAX];
vector<bitset<64> >v;

ll gauss(int n,int m)
{
    int col=m-1,row=0,i,j;
    ll ans=0;
    for(;col>=0 && row<n;col--){
        for(i=row;i<n;i++){
            if(v[i][col]){
                swap(v[i],v[row]);
                break;
            }
        }
        if(!v[row][col])continue;

        for(i=0;i<n;i++){
            if(i==row)continue;
            if(v[i][col])
                v[i]^=v[row];
        }
        row++;
    }



    return row;
}

int main()
{
    //freopen("input.txt","r",stdin);
    int i,j,n;
    ll xx=0;
    scanf("%d",&n);
    for(i=0;i<n;i++){
        scanf("%lld",&a[i]);
        xx^=a[i];
    }
    if(xx==0)return cout<<-1<<endl,0;

    for(i=0;i<n;i++){
        bitset<64>x;
        for(j=0;j<64;j++){
            if(a[i] & (1LL<<j))x[j]=1;
            else x[j]=0;
        }
        v.push_back(x);
    }

    ll ans=gauss(n,64);
    cout<<ans<<endl;
}