#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001
struct combi{
	deque<mint> kaijou;
	deque<mint> kaijou_;
	
	combi(int n){
		kaijou.push_back(1);
		for(int i=1;i<=n;i++){
			kaijou.push_back(kaijou[i-1]*i);
		}
		
		mint b=kaijou[n].inv();
		
		kaijou_.push_front(b);
		for(int i=1;i<=n;i++){
			int k=n+1-i;
			kaijou_.push_front(kaijou_[0]*k);
		}
	}
	
	mint combination(int n,int r){
		if(r>n)return 0;
		mint a = kaijou[n]*kaijou_[r];
		a *= kaijou_[n-r];
		return a;
	}
	
	mint junretsu(int a,int b){
		mint x = kaijou_[a]*kaijou_[b];
		x *= kaijou[a+b];
		return x;
	}
	
	mint catalan(int n){
		return combination(2*n,n)/(n+1);
	}
	
};

combi C(100000);
int main(){
	
	int H,W;
	cin>>H>>W;
	
	queue<vector<mint>> Q;
	rep(i,H){
		int a,b;
		cin>>a>>b;
		vector<mint> t(W+1);
		{
			mint v = 1;
			rep(j,W){
				v *= W + b - j;
				v /= j+1;
			}
			t[0] += v;
			rep(j,W){
				v /= W+j+1;
				v *= b-j;
				t[j+1] += v;
			}
		}
		if(a!=0){
			a--;
			mint v = 1;
			rep(j,W){
				v *= W + a - j;
				v /= j+1;
			}
			t[0] -= v;
			rep(j,W){
				v /= W+j+1;
				v *= a-j;
				t[j+1] -= v;
			}
		}
		/*rep(j,W+1){
			cout<<t[j].val()<<',';
		}
		cout<<endl;
		*/
		rep(j,W+1)t[j] *= C.kaijou_[j];
		Q.push(t);
	}
	
	while(Q.size()>1){
		auto a = Q.front();
		Q.pop();
		auto b = Q.front();
		Q.pop();
		a = convolution(a,b);
		while(a.size()>W+1)a.pop_back();
		Q.push(a);
	}
	mint ans = Q.front()[W];
	ans *= C.kaijou[W];
	cout<<ans.val()<<endl;
	
	return 0;
}