#include<cstdio>

#include<algorithm>

#define inf 2147483647

int n,m,statenum;

int num[],f[][];

bool pd(int state1,int state2){

    int a1=state1%,b1=,c1=,a2=state2%,b2=,c2=;

    state1/=;state2/=;

    for(int i();i<=*n;i+=){

        c1=b1;b1=a1;a1=state1%;state1/=;

        c2=b2;b2=a2;a2=state2%;state2/=;

        if(b2== && b1!=)return false;

        if(b1== && b2!=)return false;

        if(b1== && a1!= && c1!=)return false;

    }

    return true;

}

void solve(){

    statenum=(<<n*)-;

    for(int i();i<=statenum;++i)

        {f[][i]=inf;for(int j=i;j;j>>=)num[i]+=(j&)==;}

    f[][statenum]=;

    int x=,y=;

    for(int k();k<=m+;++k,x=!x,y=!y)

        for(int i();i<=statenum;++i){

            f[y][i]=inf;

            for(int j();j<=statenum;++j)

                if(f[x][j]!=inf && pd(i,j))

                    f[y][i]=std::min(f[y][i],f[x][j]+num[i]);

        }

    if(f[y][]==inf)

        printf("");else printf("%d",n*m-f[x][]);

}

int main(){

    //freopen("in.txt","r",stdin);

    //freopen("out.txt","w",stdout);

    scanf("%d %d",&n,&m);

    if(n>m)std::swap(n,m);

    solve();

    //fclose(stdin);fclose(stdout);

    return ;

}

#include<cstdio>

#define P(x)    return printf("%d\n",m*n-(x)),0;

int main(){

    //freopen("in.txt","r",stdin);

    //freopen("out.txt","w",stdout);

    int n,m;

    scanf("%d%d",&n,&m);

    if(n>m)n^=m,m^=n,n^=m;

    switch(n){

        case :P((m+)/)

        case :P((m+)/)

        case :P(m/*+(m%=)+(m==))

        case :P(m+(m==||m==||m==))

        case :P(m/*-(m==)+(m%=)++(m>))

        case :P()

    }

    fclose(stdin);fclose(stdout);

}