#include<bits/stdc++.h>
#define int long long
#define ffor(i,a,b) for(int i=(a);i<=(b);i++)
#define roff(i,a,b) for(int i=(a);i>=(b);i--)
using namespace std;
const int MAXN=2e5+10;
int n,m,x[MAXN],y[MAXN];
__int128 sum;
struct INFO {int x,y,k;__int128 sum;};
stack<INFO> st;
void insert(int X,int Y) {
	while(!st.empty()) {
		__int128 x=st.top().x,y=st.top().y,k=st.top().k;
		__int128 Ymx=y+(X-x)*k-(X-x)*(X-x+1)/2; 
		if(Ymx<Y) {st.pop();continue ;}
		__int128 dt=Ymx-Y,del=dt/(X-x),d=X-x;
		__int128 sum=y*d+k*d+k*d*d-(k+d+1)*d*(d+1)/2+d*(d+1)*(d+d+1)/6;
		sum-=del*(d*(d+1)/2),k-=del;
		k-=d;
		if(dt%d) dt%=d,sum-=d*(d+1)/2,k--;	
		st.push({X,Y,k,sum});
		break ;
	}
	return ;
}
signed main() {
	ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
	cin>>n>>m;
	ffor(i,1,n) cin>>x[i]>>y[i];
	st.push({0,0,(__int128)100000000000000000000,0});
	ffor(i,1,n) insert(x[i],y[i]);
	insert(m,0);
	while(!st.empty()) sum+=st.top().sum,st.pop();
	cout<<(int)(sum%998244353);
	return 0;
}