diff --git a/nbackseq b/nbackseq
index af68645..8f5497a 100755
--- a/nbackseq
+++ b/nbackseq
@@ -1,10 +1,28 @@
 #!/usr/bin/env python
 import sys
+import random
 
 
 def nbackseq(n, length, words):
-    pass
+    sequence = []
+    if length > n:
+        sequence.extend(random.sample(words, n))
+        while len(sequence) < length:
+            word = random.sample(words, 1)
+            while word[0] not in sequence[-n:]:
+                sequence += word[0]
+    else:
+        sequence.extend(random.sample(words, length))
+    return sequence
 
 
 if __name__ == '__main__':
-    print(sys.argv)
+    n = int(sys.argv[1])
+    length = int(sys.argv[2])
+    words = sys.argv[3:]
+    if len(words) != len(set(words)):
+        raise ValueError('Your input words are repeated')
+    if len(words) <= n:
+        raise ValueError('N-back is greater than the number of words')
+    sequence = nbackseq(n, length, words)
+    print(sequence)