diff --git a/homeworks/21_Martin_Zlatanov/02_list_replace.py b/homeworks/21_Martin_Zlatanov/02_list_replace.py
new file mode 100644
index 0000000..b3b54d1
--- /dev/null
+++ b/homeworks/21_Martin_Zlatanov/02_list_replace.py
@@ -0,0 +1,20 @@
+def replace(l, find, replacer):
+  try:
+    l = l.copy()
+    for i, item in enumerate(l):
+        if item == find:
+            l[i] = replacer
+            continue
+        elif type(l[i]) is tuple:
+          l[i] = list(l[i])
+          for i, item in enumerate(l):
+            if item == find:
+              l[i] = replacer
+        l[i] = replace(item, find, replacer)
+  finally:
+      return l
+
+
+l = [ 'a', 1, [ ['a', 'b'], 1], ([1, 3, 'a'], 'b')]
+res = replace(l, 'a', 'c')
+print(res)
\ No newline at end of file
diff --git a/homeworks/21_Martin_Zlatanov/02_stairs_num_ways.py b/homeworks/21_Martin_Zlatanov/02_stairs_num_ways.py
new file mode 100644
index 0000000..2f8950f
--- /dev/null
+++ b/homeworks/21_Martin_Zlatanov/02_stairs_num_ways.py
@@ -0,0 +1,17 @@
+def fibonacci(i):
+  if i == 1 or i == 2:
+    return i
+  return fibonacci(i-1) + fibonacci(i-2)
+  
+
+def num_ways(N):
+  if N <= 1:
+    return "Error"
+  elif N == 2:
+      return N
+  return fibonacci(N)
+    
+
+print(num_ways(3))
+print(num_ways(4))
+print(num_ways(0))