Problem:
Score : 200 points

Problem Statement

We have a board with H horizontal rows and W vertical columns of squares.
There is a bishop at the top-left square on this board.
How many squares can this bishop reach by zero or more movements?

Here the bishop can only move diagonally.
More formally, the bishop can move from the square at the r_1-th row (from the top) and the c_1-th column (from the left) to the square at the r_2-th row and the c_2-th column if and only if exactly one of the following holds:

r_1 + c_1 = r_2 + c_2

r_1 - c_1 = r_2 - c_2

For example, in the following figure, the bishop can move to any of the red squares in one move:

Constraints

1 \leq H, W \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

H \ W

Output

Print the number of squares the bishop can reach.

Sample Input 1

4 5

Sample Output 1

10

The bishop can reach the cyan squares in the following figure:

Sample Input 2

7 3

Sample Output 2

11

The bishop can reach the cyan squares in the following figure:

Sample Input 3

1000000000 1000000000

Sample Output 3

500000000000000000

Solution in Go (1.6) (judge verdict: Wrong Answer)

package main

import (
	"bufio"
	"fmt"
	"os"
	"reflect"
	"strconv"
)

const (
	maxBufSize = 1024 * 1024
)

var (
	sc = func() *bufio.Scanner {
		sc := bufio.NewScanner(os.Stdin)
		buf := make([]byte, 1)
		sc.Buffer(buf, maxBufSize)
		sc.Split(bufio.ScanWords)
		return sc
	}()
	out = bufio.NewWriter(os.Stdout)
)

func solve(h int64, w int64) int64 {
	return ((w + 1)/ 2) * ((h + 1) / 2) + (w /2 ) * (h / 2)
}

func main() {
	defer out.Flush()

	h := nextInt()
	w := nextInt()
	res := solve(h, w)
	fmt.Fprintln(out, res)
}

func next() string {
	sc.Scan()
	return sc.Text()
}

func nextStringAsBytes() []byte {
	sc.Scan()
	return []byte(sc.Text())
}

func nextInt() int64 {
	a, _ := strconv.ParseInt(next(), 10, 64)
	return a
}

func nextFloat() float64 {
	a, _ := strconv.ParseFloat(next(), 64)
	return a
}

func nextInts(n int64) []int64 {
	ret := make([]int64, n)
	for i := int64(0); i < n; i++ {
		ret[i] = nextInt()
	}
	return ret
}

func nextFloats(n int64) []float64 {
	ret := make([]float64, n)
	for i := int64(0); i < n; i++ {
		ret[i] = nextFloat()
	}
	return ret
}
func nextStrings(n int64) []string {
	ret := make([]string, n)
	for i := int64(0); i < n; i++ {
		ret[i] = next()
	}
	return ret
}

func containStr(arr []string, target string) bool {
	for _, v := range arr {
		if v == target {
			return true
		}
	}
	return false
}

func PrintOut(src interface{}, joinner string) {
	switch reflect.TypeOf(src).Kind() {
	case reflect.Slice:
		s := reflect.ValueOf(src)
		for idx := 0; idx < s.Len(); idx++ {
			fmt.Fprintf(out, "%v", s.Index(idx))
			if idx < s.Len()-1 {
				fmt.Fprintf(out, "%s", joinner)
			} else {
				fmt.Fprintln(out)
			}
		}
	default:
		fmt.Fprintln(out, "orz")
	}
}

// mapからkeysとvaluesを返す
func splitKeyValue(m map[interface{}]interface{}) (keys, values []interface{}) {
	switch reflect.TypeOf(m).Kind() {
	case reflect.Map:
		s := reflect.ValueOf(m)
		for _, v := range s.MapKeys() {
			keys = append(keys, v)
			values = append(values, s.MapIndex(v))
		}
	default:
		fmt.Fprintln(out, "orz")
	}
	return
}