int solution(int A[], int N) {
    // write your code in C99 (gcc 4.8.2)
    unsigned i, j;

        if (N == 1)
            return A[0];

        for (i = 0, j = i+1; j<=N; j++) {
            if (A[i] != 0) {
                if (A[i] == A[j])
                    A[j] = 0;
                else {
                    if (j == N-1)
                        return(A[i]);
                    continue;
                }
            }
            j = ++i;
        }
}