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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <vector>
#include <string>
#include <stdio.h>
#include<limits.h>
#include<algorithm>
#include<queue>
#include<set>


#define MOD 1000000007

using namespace std;

long long int modpow(long long int a, long long int n) {
	if (n == 0)return 1;
	if (n == 1)return (a % MOD);

	long long int hanbun = n / 2;
	long long int amari = n % 2;

	long long int ans = (a * a) % MOD;
	ans = modpow(ans, hanbun);

	if (amari == 1)ans *= a;

	ans %= MOD;

	return ans;

}

long long int gcd(long long int a, long long int b) {
	if (a < b) {
		long long int tmp = a;
		a = b;
		b = tmp;
	}

	long long int amari = a % b;

	if (amari == 0)return b;

	return gcd(b, amari);
}

long long int lcm(long long int a, long long int b) {
	long long int ans = (a * b) % MOD;
	long long int wari = modpow(gcd(a, b), MOD - 2);
	ans = (ans * wari) % MOD;
	return ans;
}

long long int factElement[10000] = { 0 };

long long int factrial(int n) {

	if (factElement[n] != 0)return factElement[n];

	if (n == 0) {
		factElement[0] = 1;
		return factElement[n];
	}

	long long int ans = n * factrial(n - 1);
	factElement[n] = ans;
	return factElement[n];

}


int main()
{

	long long int h, w;
	cin >> h >> w;

	long long int a, b;
	a = (w + 1) / 2;
	b = w / 2;

	long long int c, d;
	c = (h + 1) / 2;
	d = h / 2;

	long long int ans = a * c + b * d;
	cout << ans << endl;



	




	return 0;

}