最后打印那行为什么出bug

Question

package com.imooc.method;public class FacDemo { public int fac(int n) { int s=1; for(int i=1;i<=n;i++) { s*=i;//s=s*i; } return s; } public static void main(String[] args){ FacDemo facDemo=new FacDemo(); int fac=facDemo.fac(3); System.out.println("3!="+fac); //求1！+2！+3!+4！+5！ int sum=0; for(int i=1;1<=5;i++) { fac=facDemo.fac(i); sum=sum+fac; } System.out.println("1!+2!+3!+4!+5!"); }}