var condition_true=1;
var condition_false=0;
if(condition_true)
{
    var a=1;
}
else if(!condition_false)
{
    var b=1;
}
elsif(!condition_true and condition_false)
{
    print("impossible");
}
else
{
    var c=1;
    var d=1;
}

if(condition_true)
    var a=1;
else if(!condition_false)
    var b=1;
elsif(!condition_true and condition_false)
    print("impossible");
else
    var c=1;