getFirstAvailableBlock RPC Method

curl https://api.devnet.solana.com -s -X POST -H "Content-Type: application/json" -d '
  {
    "jsonrpc":"2.0","id":1,
    "method":"getFirstAvailableBlock"
  }
'

{ "jsonrpc": "2.0", "result": 250000, "id": 1 }