function calculate()
{
wall1_width = window.document.form1.wall1w.value;
wall1_height = window.document.form1.wall1h.value;
wall2_width = window.document.form1.wall2w.value;
wall2_height = window.document.form1.wall2h.value;
wall3_width = window.document.form1.wall3w.value;
wall3_height = window.document.form1.wall3h.value;
wall4_width = window.document.form1.wall4w.value;
wall4_height = window.document.form1.wall4h.value;

door1_width = window.document.form1.door1w.value;
door1_height = window.document.form1.door1h.value;
door2_width = window.document.form1.door2w.value;
door2_height = window.document.form1.door2h.value;

window1_width = window.document.form1.window1w.value;
window1_height = window.document.form1.window1h.value;
window2_width = window.document.form1.window2w.value;
window2_height = window.document.form1.window2h.value;

cans = window.document.form1.askcans.value;

wall1_area = wall1_width * wall1_height;
window.document.form1.wall1area.value = wall1_area;
wall2_area = wall2_width * wall2_height;
window.document.form1.wall2area.value = wall2_area;
wall3_area = wall3_width * wall3_height;
window.document.form1.wall3area.value = wall3_area;
wall4_area = wall4_width * wall4_height;
window.document.form1.wall4area.value = wall4_area;

total1_area = wall1_area + wall2_area + wall3_area + wall4_area;
window.document.form1.total1.value = total1_area;

door1_area = door1_width * door1_height;
door2_area = door2_width * door2_height;
total_door_area = door1_area + door2_area;

window1_area = window1_width * window1_height;
window2_area = window2_width * window2_height;
total_window_area = window1_area + window2_area;

total_space = total_door_area + total_window_area;

total2_area = total1_area - total_space;
window.document.form1.total2.value = total2_area;

give_cans = total2_area / cans;
window.document.form1.givecans.value = give_cans;
}