Army Game

Luke is daydreaming in Math class. He has a sheet of graph paper with n rows and m columns, and he imagines that there is an army base in each cell for a total of n.m bases. He wants to drop supplies at strategic points on the sheet, marking each drop point with a red dot. If a base contains at least one package inside or on top of its border fence, then it's considered to be supplied. 

Given n and m, what's the minimum number of packages that Luke must drop to supply all of his bases?

Example:

Input:  n = 2, m = 2
Output: 1

Approach

C++

#include <bits/stdc++.h>
using namespace std;

int gameWithCells(int n, int m)
{
    return (n + n % 2) * (m + m % 2) / 4;
}

int main()
{

    int n = 2, m = 2;

    cout << gameWithCells(n, m) << "\n";

    return 0;
}