if __name__ == '__main__':
    db = dict()
    n = int(input().strip())
    for _ in range(n):
        index, value = list(map(int, input().strip().split()))
        if index in db.keys():
            db[index] += value
        else:
            db[index] = value
    for key in sorted(db.keys()):
        print(' '.join(map(str, [key, db[key]])))