import time
import numpy as np 

def mc_plain(S, K, T, r, sigma, N): 
  # using the same seed: 
  np.random.seed(35) 
  payoffs = [] 
  for i in range(N): 
    Z = np.random.standard_normal() 
    ST = S * np.exp((r - 0.5 * sigma**2) * T + sigma * np.sqrt(T) * Z) 
    payoff = max(ST - K, 0) 
    payoffs.append(payoff) 
  return np.exp(-r * T) * np.mean(payoffs) 

