import java.util.Scanner;


public class VideoDuration {

/**
* @param args
*/
public static void main(String[] args) {
//TODO Auto-generated method stub
Scanner input = new Scanner(System.in);
int result =0;
while (true) {
String videoDuration = input.nextLine();
if (videoDuration.equals("End")) {
break;
}
String[] array = videoDuration.split(":");
int minutes = Integer.parseInt(array[1]);
int hours = Integer.parseInt(array[0]);
result += 60*hours+minutes;

}
int hours = result/60;
result = result%60;
//System.out.println(hours+":"+result);
System.out.printf("%d:%02d\n", hours, result);
}
}