diff --git a/LabMD_1/longest_substring.py b/LabMD_1/longest_substring.py
new file mode 100644
index 0000000..8034d6a
--- /dev/null
+++ b/LabMD_1/longest_substring.py
@@ -0,0 +1,55 @@
+def countTimesOfSubstringInString(substrn, strng):
+    m = len(substrn)
+    n = len(strng)
+    number = 0
+    for i in range(n - m + 1):
+        j = 0
+        while j < m:
+            if strng[i + j] != substrn[j]:
+                break
+            j += 1
+        if j == m:
+            number += 1
+    return number
+
+
+test_str = "xxxx"
+
+res = [test_str[i: j] for i in range(len(test_str))
+       for j in range(i + 1, len(test_str) + 1)]
+
+words = set()
+
+for x in res:
+    chars = []
+    strn = ''
+    for y in x:
+        if y in chars:
+            res.remove(x)
+            break
+        else:
+            chars.append(y)
+            strn += y
+        words.add(strn)
+
+nr_times = {}
+for x in words:
+    nr_times[x] = countTimesOfSubstringInString(x, test_str)
+
+max_length = 0
+for x in words:
+    if len(x) > max_length:
+        max_length = len(x)
+
+max_occurence = 0
+for x in words:
+    if nr_times[x] > max_occurence:
+        max_occurence = nr_times[x]
+print("First program output: ")
+print("Longest duplicated substrings:")
+for x in words:
+    if nr_times[x] > 1 and len(x) == max_length:
+        print(x)
+print("Second program output: ")
+print("Length of longest substring:")
+print(max_length)