unsigned long

Unsigned long variables are extended size variables for number storage, and store 32 bits (4 bytes). Unlike standard longs unsigned longs won't store negative numbers, making their range from 0 to 4,294,967,295 (2^32 - 1).

unsigned long time;
 
void setup()
{
  Serial.begin(9600);
}
 
void loop()
{
  Serial.print("Time: ");
  time = millis();
  //prints time since program started
  Serial.println(time);
  // wait a second so as not to send massive amounts of data
  delay(1000);
}

  [=unsigned long var = val;=]

*var - your long variable name *val - the value you assign to that variable

* byte * int * unsigned int * Description * Variable Declaration

Source: arduino.cc