program Main
implicit none
    integer(16) ans,a,b,c,d,x,y
    read (*,*) a, b, c, d
    x=max(a,b)
    y=max(c,d)
    if ((x>0.and.y>0)) then
        ans=x*y
    else if(x<1 .and.y<1) then
        x=min(a,b)
        y=min(b,c)
        ans=x*y
    else if(x<1) then
        y=min(c,d)
        ans=x*y
    else 
        x=min(a,b)
        ans=x*y
    end if
    write(*,*) ans
end program Main