Create q001.md for Grid Paths problem

Add problem statement for Grid Paths challenge

Author: zonedoutdg

Problems/Mathematics/Day-03/q001.md

@@ -1 +1,17 @@
+# Grid Paths
 
+There are **88418** paths in a **7 × 7** grid from the upper-left square to the lower-left square. Each path corresponds to a **48-character** description consisting of characters:
+- `D` — down  
+- `U` — up  
+- `L` — left  
+- `R` — right
+
+You are given a description of a path which may also contain characters **? (any direction)**. Your task is to calculate the **number of paths** that match the description.
+
+# INPUT
+The only input line has a 48-character string of characters ?, D, U, L and R.
+
+# OUTPUT
+Print one integer: the total number of paths.
+
+[PROBLEM LINK](https://cses.fi/problemset/task/1625)