using System;
public class Program
{
public static void Main()
Console.WriteLine(solution(7, 42, new[]{6, 42, 11, 7, 1, 42}));
}
public static int solution(int X, int Y, int[] A)
int N = A.Length;
int result = -1;
int nX = 0;
int nY = 0;
for (int i = 0; i < N; i++)
if (A[i] == X)
nX += 1;
else if (A[i] == Y)
nY += 1;
if (nX == nY)
result = i;
return result;