B'An online contest will soon be held on ForceCoders, a large competitive programming platform. The authors have prepared n problems; and since the platform is very popular, 998244351 coder from all over the world is going to solve them. For each problem, the authors estimated the number of people who would solve it: for the i -th problem, the number of accepted solutions will be between l_i and r_i , inclusive. The creator of ForceCoders uses different criteria to determine if the contest is good or bad. One of these criteria is the number of inversions in the problem order. An inversion is a pair of problems (x, y) such that x is located earlier in the contest ( x < y ), but the number of accepted solutions for y is strictly greater. Obviously, both the creator of ForceCoders and the authors of the contest want the contest to be good. Now they want to calculate the probability that there will be no inversions in the problem order, assuming that for each problem i , any integral number of accepted solutions for it (between l_i and r_i ) is equally probable, and all these numbers are independent. The first line contains one integer n ( 2 <= n <= 50 ) -- the number of problems in the contest. Then n lines follow, the i -th line contains two integers l_i and r_i ( 0 <= l_i <= r_i <= 998244351 ) -- the minimum and maximum number of accepted solutions for the i -th problem, respectively. The probability that there will be no inversions in the contest can be expressed as an irreducible fraction frac{x}{y} , where y is coprime with 998244353 . Print one integer -- the value of xy^{-1} , taken modulo 998244353 , where y^{-1} is an integer such that yy^{-1} equiv 1 (mod 998244353) . The real answer in the first test is frac{1}{2} . '...