问有一个无效的浮点运算，但是在哪里？

EN

program TwoSquares;

var
    num, numSqrt, iter, bigSqr,smallSqr: integer;
    


begin
    num:=29;
    
    while num>4 do
    begin
        numSqrt:=trunc(sqrt(num));
        for iter:=2 to numSqrt do
        begin
            if num mod iter = 0 then
                num:=num - 1;
                continue;
        end;
        
        if (num-1) mod 4 = 0 then
        begin
            iter:=(num-1) div 4;
            while iter>0 do
            begin
                if num-(iter*iter)>0 then
                    bigSqr:=iter;
                    break;
                iter:=iter-1;
            end;
            smallSqr:=trunc(sqrt(num-(iter*iter)));
            writeln(num,' ', smallSqr,' ',bigSqr);
            num:=num - 1;
        end;
    end;
end.