JOURNEY Pascal

var s:ansistring;
    d,a:array['A'..'Z'] of longint;
    x,y,i,tx,ty,k:longint;
    c:char;

procedure nhap;
begin
    readln(tx,ty);
    readln(s);
end;

procedure b1;
begin
    x:=0;y:=0;
    for i:=1 to length(s) do
    begin
        if s[i]='U' then inc(y);
        if s[i]='D' then dec(y);
        if s[i]='R' then inc(x);
        if s[i]='L' then dec(x);
        if s[i]='?' then inc(k);
    end;
end;

procedure b2;
begin
    if (x>=tx) then
    begin
        d['L']:=x-tx;
        dec(k,d['L']);
    end
    else
    begin
        d['R']:=tx-x;
        dec(k,d['R']);
    end;
    if (y>=ty) then
    begin
        d['D']:=y-ty;
        dec(k,d['D']);
    end
    else
    begin
        d['U']:=ty-y;
        dec(k,d['U']);
    end;
end;

procedure b3;
begin
    if k<0 then
    begin
        write('IMPOSSIBLE');
        halt;
    end
    else
    begin
        if k mod 2=0 then
        begin
            inc(d['D'],k div 2);
            inc(d['U'],k div 2);
        end
        else
        begin
            write('IMPOSSIBLE');
            halt;
        end;
    end;
end;

procedure b4;
begin
    for i:=1 to length(s) do
    begin
        if s[i]='?' then
        begin
            for c:='D' to 'U' do
            begin
                if d[c]>0 then
                begin
                    s[i]:=c;
                    dec(d[c]);
                    break;
                end;
            end;
        end;
    end;
    write(s);
end;

begin
    assign(input,'journey.inp');reset(input);
    assign(output,'journey.out');rewrite(output);
    nhap;
    b1;
    b2;
    b3;
    b4;
end.