#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 *);
int main() {
  int N, M;
  scanf("%d%d", &N, &M);
  if (N % 2 == 0 || M % 2 == 0) {
    printf("%d", N * M / 2);
  } else {
    printf("%d", (N * M - 1) / 2);
  }
  return 0;
}


x86 assembly (clang, -O0):
<main>:
push   %rbp
mov    %rsp,%rbp
sub    $0x10,%rsp
movl   $0x0,-0x4(%rbp)
lea    0xeca(%rip),%rdi
lea    -0x8(%rbp),%rsi
lea    -0xc(%rbp),%rdx
call   1040 <scanf@plt>
mov    -0x8(%rbp),%eax
mov    $0x2,%ecx
cltd
idiv   %ecx
cmp    $0x0,%edx
je     116b <main+0x4b>
mov    -0xc(%rbp),%eax
mov    $0x2,%ecx
cltd
idiv   %ecx
cmp    $0x0,%edx
jne    118d <main+0x6d>
mov    -0x8(%rbp),%eax
imul   -0xc(%rbp),%eax
mov    $0x2,%ecx
cltd
idiv   %ecx
mov    %eax,%esi
lea    0xe7f(%rip),%rdi
call   1030 <printf@plt>
jmp    11ad <main+0x8d>
mov    -0x8(%rbp),%eax
imul   -0xc(%rbp),%eax
sub    $0x1,%eax
mov    $0x2,%ecx
cltd
idiv   %ecx
mov    %eax,%esi
lea    0xe5a(%rip),%rdi
call   1030 <printf@plt>
xor    %eax,%eax
add    $0x10,%rsp
pop    %rbp
ret

x86 assembly (clang, -O2):
<main>:
push   %rax
lea    0xed8(%rip),%rdi
lea    0x4(%rsp),%rsi
mov    %rsp,%rdx
call   1040 <scanf@plt>
mov    0x4(%rsp),%eax
mov    (%rsp),%ecx
mov    %eax,%edx
and    %ecx,%edx
and    $0x1,%edx
imul   %eax,%ecx
sub    %edx,%ecx
mov    %ecx,%esi
shr    $0x1f,%esi
add    %ecx,%esi
sar    %esi
lea    0xeaa(%rip),%rdi
call   1030 <printf@plt>
xor    %eax,%eax
pop    %rcx
ret

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

LLVM IR (-O2):
@.str = [5 x i8] c"%d%d\00"
@.str.1 = [3 x i8] c"%d\00"
define i32 @main() {
%1 = alloca i32
%2 = alloca i32
%3 = bitcast i32* %1 to i8*
%4 = bitcast i32* %2 to i8*
%5 = call i32 @scanf(i8* getelementptr inbounds ([5 x i8], [5 x i8]* @.str, i64 0, i64 0), i32* %1, i32* %2)
%6 = load i32, i32* %1
%7 = and i32 %6, 1
%8 = icmp ne i32 %7, 0
%9 = load i32, i32* %2
%10 = and i32 %9, 1
%11 = icmp ne i32 %10, 0
%12 = select i1 %8, i1 %11, i1 false
%13 = mul nsw i32 %9, %6
%14 = sext i1 %12 to i32
%15 = add nsw i32 %13, %14
%16 = sdiv i32 %15, 2
%17 = call i32 @printf(i8* getelementptr inbounds ([3 x i8], [3 x i8]* @.str.1, i64 0, i64 0), i32 %16)
ret i32 0
}