diff --git a/app/main.py b/app/main.py
index 49d45fd..6c8ef7c 100644
--- a/app/main.py
+++ b/app/main.py
@@ -4,34 +4,42 @@ import asyncio
 from schemas.api_schemas import *
 from mongo_worker import MongoWorker
 
-from typing import Annotated
-
-from fastapi import FastAPI, Depends, UploadFile, File
+from fastapi import FastAPI, Depends, Response, status
 
 
 app = FastAPI()
 
-@app.get("/check_user")
-async def check_user(user_id: int,
+@app.get("/check_user", status_code=200)
+async def check_user(user_id: NonNegativeInt,
                      mongo: MongoWorker = Depends(MongoWorker)) -> BaseResponse:
     result = mongo.check_user(user_id)
     return BaseResponse(result=result)
 
-@app.get("/get_user")
-async def get_user(user_id: int,
+@app.get("/get_user", status_code=200)
+async def get_user(user_id: NonNegativeInt,
+                   response: Response,
                    mongo: MongoWorker = Depends(MongoWorker)) -> BaseResponse:
-    result = mongo.get_user(user_id)
-    return BaseResponse(result=result)
+    if mongo.check_user(user_id):
+        result = mongo.get_user(user_id)
+        return BaseResponse(result=result)
+    else:
+        response.status_code = status.HTTP_404_NOT_FOUND
+        return BaseResponse(result="User doesn't exist", error=True)
 
-@app.post("/add_user")
+@app.post("/add_user", status_code=201)
 async def add_user(new_user: AddUserBody,
+                   response: Response,
                    mongo: MongoWorker = Depends(MongoWorker)) -> BaseResponse:
-    result = mongo.add_user(new_user.user_id,
-                            new_user.username,
-                            new_user.first_name,
-                            new_user.last_name,
-                            new_user.photo_url)
-    return BaseResponse(result=result)
+    if not mongo.check_user(new_user.user_id):
+        result = mongo.add_user(new_user.user_id,
+                                new_user.username,
+                                new_user.first_name,
+                                new_user.last_name,
+                                new_user.photo_url)
+        return BaseResponse(result=result)
+    else:
+        response.status_code = status.HTTP_409_CONFLICT
+        return BaseResponse(result="User already exist", error=True)
 
 
 async def main():
diff --git a/app/schemas/api_schemas.py b/app/schemas/api_schemas.py
index 386a51a..5b117e1 100644
--- a/app/schemas/api_schemas.py
+++ b/app/schemas/api_schemas.py
@@ -1,6 +1,6 @@
 import typing
 
-from pydantic import BaseModel
+from pydantic import BaseModel, NonNegativeInt
 
 
 class BaseResponse(BaseModel):
@@ -8,7 +8,7 @@ class BaseResponse(BaseModel):
     error: bool = False
 
 class AddUserBody(BaseModel):
-    user_id: int
+    user_id: NonNegativeInt
     username: str
 
     first_name: str