def solve(ab):
    sa = sum(a for a,b in ab)
    sb = sum(b for a,b in ab)

    min_b0 = max(max(a+b for a,b in ab) - sb, 0)
    return sb-max(0, min_b0-sa+sb)+1


n = int(input())
ab = [tuple(map(int,input().split())) for _ in range(n-1)]
print(solve(ab))