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!");

}

}