Help to delimit and read specific contents of incoming HTTP string I am sending strings to an Esp8266 via web browser.

The below code returns the following in serial monitor if I send in browser: 

Send from browser to esp8266 - http://192.168.1.220/s1s2s3s4s5d1
Receive in Arduino Serial monitor - GET /s1s2s3s4s5d2 HTTP/1.1

How do i read only the contents s1s2s3s4s5d1  ? This content can vary in length, numbers could be double digits but alphabets will remain in between.

Please note I am still a novice. 


// Read the first line of the request
String request = client.readStringUntil('\r');
Serial.println(request);
client.flush();
I have this

if (client.connected()) {
  if (client.available() &amp;&amp; client.find(' ')) { // GET /fn HTTP/1.1
    char fn[20];
    int l = client.readBytesUntil(' ', fn, sizeof(fn));
    fn[l] = 0;
    while (client.read() != -1);
    Serial.println(fn);
    client.stop(); 
  }
}