#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 /*<<< orphan*/ scanf(char *, int *);
int main(int argc, char *argv[]) {
  int n, i;
  scanf("%d", &n);
  if (n == 1)
    printf("-1\n");
  else if (n & 1) {
    printf("-1\n");
  } else {
    for (i = 1; i < n; i += 2)
      printf("%d %d ", i + 1, i);
  }
  return 0;
}


x86 assembly (clang, -O0):
<main>:
push   %rbp
mov    %rsp,%rbp
sub    $0x20,%rsp
movl   $0x0,-0x4(%rbp)
mov    %edi,-0x8(%rbp)
mov    %rsi,-0x10(%rbp)
lea    0xec3(%rip),%rdi
lea    -0x14(%rbp),%rsi
call   1040 <scanf@plt>
cmpl   $0x1,-0x14(%rbp)
jne    1163 <main+0x43>
lea    0xeac(%rip),%rdi
mov    $0x0,%al
call   1030 <printf@plt>
jmp    11c7 <main+0xa7>
mov    -0x14(%rbp),%eax
and    $0x1,%eax
cmp    $0x0,%eax
je     1185 <main+0x65>
lea    0xe8a(%rip),%rdi
mov    $0x0,%al
call   1030 <printf@plt>
jmp    11c2 <main+0xa2>
movl   $0x1,-0x18(%rbp)
mov    -0x18(%rbp),%eax
cmp    -0x14(%rbp),%eax
jge    11bd <main+0x9d>
mov    -0x18(%rbp),%esi
add    $0x1,%esi
mov    -0x18(%rbp),%edx
lea    0xe5f(%rip),%rdi
mov    $0x0,%al
call   1030 <printf@plt>
mov    -0x18(%rbp),%eax
add    $0x2,%eax
mov    %eax,-0x18(%rbp)
jmp    118c <main+0x6c>
jmp    11c2 <main+0xa2>
jmp    11c7 <main+0xa7>
xor    %eax,%eax
add    $0x20,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<main>:
push   %r14
push   %rbx
push   %rax
lea    0xec5(%rip),%rdi
lea    0x4(%rsp),%rsi
call   1050 <scanf@plt>
mov    0x4(%rsp),%eax
cmp    $0x1,%eax
je     118a <main+0x5a>
test   $0x1,%al
jne    118a <main+0x5a>
cmp    $0x2,%eax
jl     1196 <main+0x66>
mov    $0x1,%ebx
lea    0xea0(%rip),%r14
cs nopw 0x0(%rax,%rax,1)
nopl   (%rax)
lea    0x1(%rbx),%esi
mov    %r14,%rdi
mov    %ebx,%edx
xor    %eax,%eax
call   1040 <printf@plt>
add    $0x2,%ebx
cmp    0x4(%rsp),%ebx
jl     1170 <main+0x40>
jmp    1196 <main+0x66>
lea    0xe79(%rip),%rdi
call   1030 <puts@plt>
xor    %eax,%eax
add    $0x8,%rsp
pop    %rbx
pop    %r14
ret

LLVM IR (-O0):
@.str = [3 x i8] c"%d\00"
@.str.1 = [4 x i8] c"-1\0A\00"
@.str.2 = [7 x i8] c"%d %d \00"
define i32 @main(i32 %0, i8** %1) {
%3 = alloca i32
%4 = alloca i32
%5 = alloca i8**
%6 = alloca i32
%7 = alloca i32
store i32 0, i32* %3
store i32 %0, i32* %4
store i8** %1, i8*** %5
%8 = call i32 @scanf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str, i64 0, i64 0), i32* %6)
%9 = load i32, i32* %6
%10 = icmp eq i32 %9, 1
br i1 %10, label %11, label %13
11: ; preds = %2
%12 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0))
br label %34
13: ; preds = %2
%14 = load i32, i32* %6
%15 = and i32 %14, 1
%16 = icmp ne i32 %15, 0
br i1 %16, label %17, label %19
17: ; preds = %13
%18 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str.1, i64 0, i64 0))
br label %33
19: ; preds = %13
store i32 1, i32* %7
br label %20
20: ; preds = %29, %19
%21 = load i32, i32* %7
%22 = load i32, i32* %6
%23 = icmp slt i32 %21, %22
br i1 %23, label %24, label %32
24: ; preds = %20
%25 = load i32, i32* %7
%26 = add nsw i32 %25, 1
%27 = load i32, i32* %7
%28 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([7 x i8], [7 x i8]* @.str.2, i64 0, i64 0), i32 %26, i32 %27)
br label %29
29: ; preds = %24
%30 = load i32, i32* %7
%31 = add nsw i32 %30, 2
store i32 %31, i32* %7
br label %20
32: ; preds = %20
br label %33
33: ; preds = %32, %17
br label %34
34: ; preds = %33, %11
ret i32 0
}

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