#include <algorithm>

#include <cstdio>

#define maxn 2010

const int mod = 998244353;

namespace Math {

	inline int pw(int base, int p) {

		static int res;

		for (res = 1; p; p >>= 1, base = static_cast<long long> (base) * base % mod) if (p & 1) res = static_cast<long long> (res) * base % mod;

		return res;

	}

	inline int inv(int x) { return pw(x, mod - 2); }

}

inline void reduce(int &x) { x += x >> 31 & mod; }

inline int getreduce(int x) { return x + (x >> 31 & mod); }

int n, k, ans;

int x[maxn], y[maxn];

int main() {

	scanf("%d%d", &n, &k);

	for (int i = 1; i <= n; ++i) scanf("%d%d", x + i, y + i);

	for (int i = 1; i <= n; ++i) {

		long long a = y[i], b = 1;

		for (int j = 1; j <= n; ++j) if (i != j) {

			a = a * getreduce(k - x[j]) % mod;

			b = b * getreduce(x[i] - x[j]) % mod;

		}

		reduce(ans += a * Math::inv(b) % mod - mod);

	}

	printf("%d\n", ans);

	return 0;

}