kill(all)$

van=facebook.com/LearningCalculus$

f(x):=floor((x-1)/4)+floor((x-2)/3)-floor((x-3)/2);

[f(-10),f(-9)];
[f( -7),f(-5)];
[f( -4),f( 2)];
[f(  3),f( 5)];
[f(  7),f( 8)];

[-10,-9);
[ -7,-5);
[ -4, 2);
[  3, 5);
[  7, 8);