For JS this worked:

function main() {
  const S = readLine();
  try {
    const num = JSON.parse(S);
    console.log(num);
  } catch (e) {
    console.log("Bad String");
  }
}

I tried this: 

S = input()

try:
    num=int(S)
    print(num)
except ValueError: 
    print("Bad String")

and this:

S = input()

try:
    num=int(S)
    print(num)
except: 
    raise Exception("Bad String")

` None of these worked.