// you can also use imports, for example:
// import java.util.*;

// you can write to stdout for debugging purposes, e.g.
// System.out.println("this is a debug message");

class Solution {
    public int solution(int[] A) {
        // Implement your solution here
    }
}

import Foundation
import Glibc

// you can write to stdout for debugging purposes, e.g.
// print("this is a debug message")

public func solution(_ A : inout [Int]) -> Int {
    // Implement your solution here
}

import Foundation
import Glibc

// you can write to stdout for debugging purposes, e.g.
// print("this is a debug message")

public func solution(_ A : inout [Int]) -> Int {
    var dict: [Int: (Int, Int)] = [:]
    
    if A.count == 1 { return A.first! }
    if A.count == 0 { return -1 }
    
    for (index, i) in A.enumerated() {
        if dict[i] == nil {
            dict[i] = (index, 1)
        } else {
            dict[i]!.1 += 1
        }
    }
    
    dict = dict.filter({ $0.value.1 == 1 })
    return dict.sorted(by: { $0.value.0 < $1.value.0 }).first?.key ?? -1
}

import Foundation
import Glibc

// you can write to stdout for debugging purposes, e.g.
// print("this is a debug message")

public func solution(_ A : inout [Int]) -> Int {
    var dict: [Int: (Int, Int)] = [:]
    
    if A.count == 1 { return A.first! }
    if A.count == 0 { return -1 }
    
    for (index, i) in A.enumerated() {
        if dict[i] == nil {
            dict[i] = (index, 1)
        } else {
            dict[i]!.1 += 1
        }
    }
    
    dict = dict.filter({ $0.value.1 == 1 })
    return dict.sorted(by: { $0.value.0 < $1.value.0 }).first?.key ?? -1
}

import Foundation
import Glibc

// you can write to stdout for debugging purposes, e.g.
// print("this is a debug message")

public func solution(_ A : inout [Int]) -> Int {
    var dict: [Int: (Int, Int)] = [:]
    
    if A.count == 1 { return A.first! }
    if A.count == 0 { return -1 }
    
    for (index, i) in A.enumerated() {
        if dict[i] == nil {
            dict[i] = (index, 1)
        } else {
            dict[i]!.1 += 1
        }
    }
    
    dict = dict.filter({ $0.value.1 == 1 })
    return dict.sorted(by: { $0.value.0 < $1.value.0 }).first?.key ?? -1
}

import Foundation
import Glibc

// you can write to stdout for debugging purposes, e.g.
// print("this is a debug message")

public func solution(_ A : inout [Int]) -> Int {
    var dict: [Int: (Int, Int)] = [:]
    
    if A.count == 1 { return A.first! }
    if A.count == 0 { return -1 }
    
    for (index, i) in A.enumerated() {
        if dict[i] == nil {
            dict[i] = (index, 1)
        } else {
            dict[i]!.1 += 1
        }
    }
    
    dict = dict.filter({ $0.value.1 == 1 })
    return dict.sorted(by: { $0.value.0 < $1.value.0 }).first?.key ?? -1
}