The sequence of \textbf{n} positive integers is given. Determines whether the sequence is a permutation of the first \textbf{n} natural numbers. \InputFile One line specifies the number \textbf{n} (\textbf{n }≤ \textbf{10000}) and \textbf{n} positive integers separated by space. It is known that each positive integer is less than \textbf{2000000.} \OutputFile Print \textbf{0}, if the sequence is a permutation. Otherwise print the minimum number that is not in the sequence.