计算PBD数的算法问题，怎么采用C语言的程序编写流程的思想去实现才能解决？

Question

Problem Description
PrisonBreak is a popular TV programme in HDU. ACboy likes it very much, and he join a PrisonBreak discussing team called "PBD".Every Tuesday night, a lot of PBDers will contact with each other to discuss the newest plot of PrisonBreak season2. Generally speaking, every PBDer has distinct ideas about the play, so everyone want to know all the others' ideas. For example, when ACboy contract with Sam, ACboy will tell all the ideas he konws to Sam, and Sam will also tell all the ideas he konws to ACboy, and the call costs 5 yuan.
If there are N people in the "PBD" team, what is the minimum cost to let everyone knows all the others' ideas?

Input
The input contains multiple test cases.
Each test case contains a number N, means there are N people in the "PBD" team.N = 0 ends the input.(A call cost 5 yuan).

Output
for each case, output a integer represent the minimum cost to let everyone knows all the others' ideas.

Sample Input
1
2
3
4
0

Sample Output
0
5
15
20