// CPP implementation of above approach

#include <bits/stdc++.h>

using namespace std;

// Function to find minimum operations

// required to make array beautiful

int minOperations(int A[], int n)

{

    if (n & 1)

        return -1;

    int zeros = 0, consZeros = 0, ones = 0;

    for (int i = 0; i < n; ++i) {

        A[i] == 0 ? zeros++ : ones++;

        // counting consecutive zeros.

        if (i + 1 < n) {

            if (A[i] == 0 && A[i + 1] == 0)

                consZeros++;

        }

    }

    // check that start and end are same

    if (A[0] == A[n - 1] && A[0] == 0)

        consZeros++;

    // check is zero and one are equal

    if (zeros == ones)

        return consZeros;

    else

        return -1;

}

// Driver program

int main()

{

    int A[] = { 1, 1, 0, 0 };

    int n = sizeof(A) / sizeof(A[0]);

    cout << minOperations(A, n);

    return 0;

}