You are given a rectangular board of *M* × *N* squares. Also you are given an unlimited number of standard domino pieces of 2 × 1 squares. You are allowed to rotate the pieces. You are asked to place as many dominoes as possible on the board so as to meet the following conditions:

1. Each domino completely covers two squares.

2. No two dominoes overlap.

3. Each domino lies entirely inside the board. It is allowed to touch the edges of the board.

Find the maximum number of dominoes, which can be placed under these restrictions.
In a single line you are given two integers *M* and *N* — board sizes in squares (1 ≤ *M* ≤ *N* ≤ 16).
a=int(input())
b=int(input())
print(int(a*b/2))a//{{{ template
#include <cstdio>
#include <algorithm>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <queue>
#include <set>
#include <vector>
#include <map>
#include <cassert>
#include <deque>
#include <cmath>
using namespace std;
#define getchar() (p1==p2&&(p2=(p1=buf)+fread(buf,1,1<<21,stdin),p1==p2)?EOF:*p1++)
char buf[1 << 21], *p1 = buf, *p2 = buf;
inline int gi(){
	char tmp=getchar();int ans=0,flag=1;
	while(!isdigit(tmp)){
		if(tmp == '-') flag = -1;
		tmp = getchar();
	}
	while(isdigit(tmp)){
		ans = ans * 10 + tmp - '0';
		tmp = getchar();
	}
	return ans * flag;
}
inline void in(int &x){x=gi();}
inline void in2(int &x,int &y){in(x),in(y);}
inline void in3(int &x,int &y,int &z){in(x),in(y),in(z);}
inline void in4(int &x,int &y,int &z,int &a){in3(x,y,z),in(a);}
inline void smax(int &x,int y){x=max(x,y);}
inline void smin(int &x,int y){x=min(x,y);}
#define MEM(arr,v) memset(arr,v,sizeof arr)
#define COPY(arr,goal) memcpy(arr,goal,sizeof goal)
#define For(i,a,b) for(int i=(int)(a);i<=(int)(b);++i)
// }}}
const int N = 300200;
int Len[N],Ch[N][27],Fail[N];
int Tag[N];
int node = 1, lst = 1;
void Build(int c,int color){
	if(Ch[lst][c] && Len[lst] + 1 == Len[Ch[lst][c]]){
		Tag[Ch[lst][c]] = -1;
		lst = Ch[lst][c];
		return;
	}
	int p = ++node,f = lst;lst = p;
	Tag[p] = color;
	Len[p] = Len[f] + 1;
	while(!Ch[f][c] && f)
		Ch[f][c] = p,f = Fail[f];
	if(!f){
		Fail[p] = 1;
		return ;
	}
	int x = Ch[f][c];
	if(Len[f] + 1 == Len[x]){
		Fail[p] = x;
		return ;
	}
	int y = ++node;
	memcpy(Ch[y],Ch[x],sizeof Ch[x]);
	Len[y] = Len[f] + 1;
	Fail[y] = Fail[x]; Fail[x] = Fail[p] = y;
	while(f && Ch[f][c] == x){
		Ch[f][c] = y;
		f = Fail[f];
	}
	return;
}
char S[N];
long long  Ans[N];
struct Edg{
	int v,nxt;
}Edge[N<<1];int Head[N];
void Add(int u,int v){
	static int cnt = 0;
	Edge[++cnt].v = v;Edge[cnt].nxt = Head[u];
	Head[u] = cnt;
}
void Dfs(int pos){
	for(int i = Head[pos]; i; i = Edge[i].nxt){
		int arr = Edge[i].v;
		Dfs(arr);
		if(Tag[arr] == -1) {Tag[pos] = -1;continue;}
		if(!Tag[pos]){
			Tag[pos] = Tag[arr];
			continue;
		}
		if(Tag[pos] != Tag[arr])
			Tag[pos] = -1;
	}
	if(Tag[pos] == 3){
		// printf("%d %d\n",Len[pos],Len[Fail[pos]]);
	}
	if(Tag[pos] != -1)
	Ans[Tag[pos]] += Len[pos] - Len[Fail[pos]];
}
signed main()
{
#ifdef DMYTXDY
	freopen("data.in","r",stdin);
#endif
	int a,b;
	in2(a,b);
	printf("%d",a*b/2);
	return 0;
	int n;cin>>n;
	For(i,1,n){
		scanf("%s",S);
		int len = strlen(S);
		For(j,0,len-1)
			Build(S[j] - 'a',i);
		lst = 1;
	}
	For(i,1,node)
		Add(Fail[i],i);
	Dfs(1);
	For(i,1,n)
		printf("%lld\n",Ans[i]);
	return 0;
}