https://www.spoj.com/problems/ADASEA/ Anyone who can give me an explanation. I am not able to comprehend

You are given three coins numbered 1, 2, and 3. Your objective is to make the number n=10 using these coins, but you cannot select the same coin consecutively. For instance, combinations like 1+2+2 or 2+2+3 are not valid but 1+2+3 or 1+2+1 valid. coins can be any type of coins and n can be any number. Find the number of ways to achieve this.