Add problem statement for GCD summation challenge

Added problem description, input/output format, constraints, and sample cases for the summation problem involving GCD.

Author: Dheeraj-06

Problems/Mathematics/Day-02/q003.md

@@ -0,0 +1,60 @@
+## Problem Description
+
+You are given a single integer `N`.
+
+You are asked to compute the following summation:
+
+Σ(i=1 to N) Σ(j=1 to N) Σ(k=1 to i) Σ(l=1 to j) (gcd(k, i) × gcd(l, j) × gcd(i, j))
+
+Output the value of this summation **modulo 1000000007**.
+
+---
+
+## Input Format
+
+- The input consists of a single integer `N`.
+
+---
+
+## Output Format
+
+- Output the value of the summation modulo `1000000007`.
+
+---
+
+## Constraints
+
+- 1 ≤ N ≤ 10^6
+
+---
+
+
+## Sample Input 1
+
+```
+2
+```
+---
+
+## Output
+
+```
+25
+```
+---
+
+## Sample Input 2
+
+```
+8
+```
+---
+
+## Output
+
+```
+13348
+```
+---
+
+[PROBLEM LINK](https://www.codechef.com/problems/YETGCD?tab=statement)