diff --git a/python/s1/s1_a4.py b/python/s1/s1_a4.py
new file mode 100644
index 0000000..3f38621
--- /dev/null
+++ b/python/s1/s1_a4.py
@@ -0,0 +1,5 @@
+n = int(input("Enter n:"))
+s = 0.0
+for i in range (1, n + 1):
+    s = s + 1.0 / (i * i)
+print(s)
\ No newline at end of file
diff --git a/python/s1/s1_a51.py b/python/s1/s1_a51.py
index f2422cb..5c9fc9f 100644
--- a/python/s1/s1_a51.py
+++ b/python/s1/s1_a51.py
@@ -1,4 +1,19 @@
 import numpy as np
 a=np.array([[3,0,-2,11],[0,0,9,0],[0,7,0,0],[0,0,0,-3]])
 
-print(a)
\ No newline at end of file
+print(a)
+
+my_list = [[], [], [], []]
+MAX_LENGTH = 4
+for i in range(0, MAX_LENGTH):
+    for j in range(0, MAX_LENGTH):
+        n = int(input("Enter n:"))
+        my_list[i].insert(j, n)
+        
+    print(my_list)  
+
+print()
+for i, row in enumerate(my_list):
+    for j, item in enumerate(row):
+        print(f'a[{i}] [{j}] = {item} ', end=' ')
+    print()
\ No newline at end of file