input: Write a python function to find the most populated city.
  assert most_populated_city({"Lahore": 3883, "Karachi": 8130, "Islamabad": 2572}) == "Karachi"
  assert most_populated_city({"New York": 8400, "Los Angeles": 4000, "Chicago": 2715}) == "New York"
  assert most_populated_city({"Tokyo": 37400, "Delhi": 29300, "Shanghai": 26300}) == "Tokyo"
output: def most_populated_city(city_population):
      return max(city_population, key=city_population.get)