from math import inf


def main():
    passengers = []
    for _ in range(int(input())-1):
        dep, arr = map(int, input().split())
        passengers.append((dep, arr))

    dep_sum = sum(dep for dep, _ in passengers)
    arr_sum = sum(arr for _, arr in passengers)

    A_dep_maximum = arr_sum
    A_arr_maximum = dep_sum

    A_dep_minimum = 0
    A_arr_minimum = 0
    for dep, arr in passengers:
        arr_rest = arr_sum - arr
        A_arr_minimum = max(A_arr_minimum, dep - arr_rest)

        dep_rest = dep_sum - dep
        A_dep_minimum = max(A_dep_minimum, arr - dep_rest)

    diff = dep_sum - arr_sum

    if A_dep_minimum + diff <= A_arr_minimum:
        print(A_arr_maximum - A_arr_minimum + 1)
    else:
        print(A_dep_maximum - A_dep_minimum + 1)


if __name__ == "__main__":
    main()