diff --git a/main.py b/main.py
new file mode 100644
index 0000000..7f83495
--- /dev/null
+++ b/main.py
@@ -0,0 +1,42 @@
+import sys
+num = '0123456789'
+uc = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+lc = 'abcdefghijklmnopqrstuvwxyz'
+
+
+def rewrite(dictionary: str, i: str, key: int, finish_str: list):
+    a = (dictionary.index(i) + key) % len(dictionary)
+    finish_str.append(dictionary[a])
+
+
+def caesar(de: str, string_to_work: str, key: int) -> str:
+    finish_str = []
+    if de == 'd':
+        key = -key
+    elif de != 'e':
+        print("Not expected value d/e:", de)
+        sys.exit(-1)
+    for i in string_to_work:
+        if i in num:
+            rewrite(num, i, key, finish_str)
+        elif i in uc:
+            rewrite(uc, i, key, finish_str)
+        elif i in lc:
+            rewrite(lc, i, key, finish_str)
+        else:
+            print("Invalid symbol:", i)
+            sys.exit(-1)
+    return "".join(finish_str)
+
+
+def main(arg: list):
+    if len(arg) != 4:
+        print("Wrong number of values", len(arg))
+        sys.exit(-1)
+    print("Old value:", arg[2])
+    print("New value:", caesar(arg[1], arg[2], int(arg[3])))
+    print("dec value:", caesar(arg[1], caesar(arg[1], arg[2], int(arg[3])), -int(arg[3])))
+
+
+if __name__ == '__main__':
+    main(sys.argv)
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