#define NULL ((void *)0)
typedef unsigned long size_t; // Customize by platform.
typedef long intptr_t;
typedef unsigned long uintptr_t;
typedef long scalar_t__; // Either arithmetic or pointer type.
/* By default, we understand bool (as a convenience). */
typedef int bool;
#define false 0
#define true 1

/* Forward declarations */

/* Type definitions */

/* Variables and functions */
int /*<<< orphan*/ printf(char *, int);
int /*<<< orphan*/ scanf(char *, int *);
int main() {
  int n;
  scanf("%d", &n);
  int s;
  scanf("%d", &s);
  int t;
  int i;
  for (i = 1; i < 2 * n + 1; ++i) {
    scanf("%d", &t);
    s ^= t;
  }
  printf("%d\n", s);
  return 0;
}


x86 assembly (clang, -O0):
<main>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
movl   $0x0,-0x4(%rbp)
lea    0xeca(%rip),%rdi
lea    -0x8(%rbp),%rsi
call   1040 <scanf@plt>
lea    0xeba(%rip),%rdi
lea    -0xc(%rbp),%rsi
call   1040 <scanf@plt>
movl   $0x1,-0x14(%rbp)
mov    -0x14(%rbp),%eax
mov    -0x8(%rbp),%ecx
shl    $0x1,%ecx
add    $0x1,%ecx
cmp    %ecx,%eax
jge    1191 <main+0x71>
lea    0xe8f(%rip),%rdi
lea    -0x10(%rbp),%rsi
call   1040 <scanf@plt>
mov    -0x10(%rbp),%eax
xor    -0xc(%rbp),%eax
mov    %eax,-0xc(%rbp)
mov    -0x14(%rbp),%eax
add    $0x1,%eax
mov    %eax,-0x14(%rbp)
jmp    1156 <main+0x36>
mov    -0xc(%rbp),%esi
lea    0xe68(%rip),%rdi
call   1030 <printf@plt>
xor    %eax,%eax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<main>:
push   %rbp
push   %r14
push   %rbx
sub    $0x10,%rsp
lea    0xed1(%rip),%rbx
lea    0x8(%rsp),%rsi
mov    %rbx,%rdi
call   1040 <scanf@plt>
lea    0x4(%rsp),%rsi
mov    %rbx,%rdi
call   1040 <scanf@plt>
mov    0x8(%rsp),%eax
add    %eax,%eax
add    $0x1,%eax
cmp    $0x2,%eax
jl     1199 <main+0x79>
mov    $0x1,%ebp
lea    0xe9d(%rip),%r14
lea    0xc(%rsp),%rbx
nopl   0x0(%rax,%rax,1)
mov    %r14,%rdi
mov    %rbx,%rsi
call   1040 <scanf@plt>
mov    0x4(%rsp),%esi
xor    0xc(%rsp),%esi
mov    %esi,0x4(%rsp)
add    $0x1,%ebp
mov    0x8(%rsp),%eax
add    %eax,%eax
add    $0x1,%eax
cmp    %eax,%ebp
jl     1170 <main+0x50>
jmp    119d <main+0x7d>
mov    0x4(%rsp),%esi
lea    0xe5f(%rip),%rdi
call   1030 <printf@plt>
xor    %eax,%eax
add    $0x10,%rsp
pop    %rbx
pop    %r14
pop    %rbp
ret

LLVM IR (-O0):
@.str = [3 x i8] c"%d\00"
@.str.1 = [4 x i8] c"%d\0A\00"
define i32 @main() {
%1 = alloca i32
%2 = alloca i32
%3 = alloca i32
%4 = alloca i32
%5 = alloca i32
store i32 0, i32* %1
%6 = call i32 @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %2)
%7 = call i32 @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %3)
store i32 1, i32* %5
br label %8
8: ; preds = %19, %0
%9 = load i32, i32* %5
%10 = load i32, i32* %2
%11 = mul nsw i32 2, %10
%12 = add nsw i32 %11, 1
%13 = icmp slt i32 %9, %12
br i1 %13, label %14, label %22
14: ; preds = %8
%15 = call i32 @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %4)
%16 = load i32, i32* %4
%17 = load i32, i32* %3
%18 = xor i32 %17, %16
store i32 %18, i32* %3
br label %19
19: ; preds = %14
%20 = load i32, i32* %5
%21 = add nsw i32 %20, 1
store i32 %21, i32* %5
br label %8
22: ; preds = %8
%23 = load i32, i32* %3
%24 = call i32 @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i32 %23)
ret i32 0
}

LLVM IR (-O2):
@.str = [3 x i8] c"%d\00"
@.str.1 = [4 x i8] c"%d\0A\00"
define i32 @main() {
%1 = alloca i32
%2 = alloca i32
%3 = alloca i32
%4 = bitcast i32* %1 to i8*
%5 = call i32 @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %1)
%6 = bitcast i32* %2 to i8*
%7 = call i32 @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %2)
%8 = bitcast i32* %3 to i8*
%9 = load i32, i32* %1
%10 = shl nsw i32 %9, 1
%11 = or i32 %10, 1
%12 = icmp sgt i32 %11, 1
br i1 %12, label %15, label %13
13: ; preds = %0
%14 = load i32, i32* %2
br label %26
15: ; preds = %0, %15
%16 = phi i32 [ %21, %15 ], [ 1, %0 ]
%17 = call i32 @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %3)
%18 = load i32, i32* %3
%19 = load i32, i32* %2
%20 = xor i32 %19, %18
store i32 %20, i32* %2
%21 = add nuw nsw i32 %16, 1
%22 = load i32, i32* %1
%23 = shl nsw i32 %22, 1
%24 = or i32 %23, 1
%25 = icmp slt i32 %21, %24
br i1 %25, label %15, label %26
26: ; preds = %15, %13
%27 = phi i32 [ %14, %13 ], [ %20, %15 ]
%28 = call i32 @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0), i32 %27)
ret i32 0
}