求用PASCAL编程 统计某个自然数区间,到底有多少个3的倍数,

program Project1;
var
m,n,x,i:Integer;
begin
Readln(m,n);
x := 0;
for i := m to n do
if i mod 3 = 0 then Inc(x);
Writeln(x);
Readln;
end.