title: represent a number as sum of four positive integer 1<a<=b<=c<=d
body: <p>Given N=a+b+c+d where a,b,c,d are positive integers greater than 0 and a&lt;=b&lt;=c&lt;=d.</p>
  
  <p>We have to count the number of ways to express N as sum of 4 such numbers. </p>
  
  <p>My approach is to have four loops and add them to n .
  But time complexity will be O(n^4) 
  Can we reduce it ?</p>