Given this Deployment YAML snippet, how many Pods will be running after applying it?

Given this Deployment YAML snippet, how many Pods will be running after applying it?

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
spec:
  replicas: 4
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: web-container
        image: nginx