On the National Day, 81 colored lanterns were hung at the factory gate from beginning to end. The distance between each two colored lanterns was 5 decimeters. How many decimeters is the width of the factory gate?
国庆节在厂门口挂彩灯，从头到尾一共挂了81只，每两只彩灯之间都相距5分米，问厂门宽多少分米？
<result>80</result>