#include <bits/stdc++.h>
#include <atcoder/all>
#define rep(i,n) for (int i = 0; i < int(n); ++i)
#define repb(i,n) for (int i = int(n)-1; i >= 0; --i)
using namespace std;
using namespace atcoder;
using ll = long long;
using mint = modint998244353;

int main(){
    int n; cin >> n;
    ll X; cin >> X;
    mint z = X;
    vector<mint> x(n);
    vector<mint> y(n);
    rep(i,n){
        ll a, b; cin >> a >> b;
        x[i] = a;
        y[i] = b;
    }
    vector<mint> lrui(n+1,1);
    vector<mint> rrui(n+1,1);
    rep(i,n) lrui[i+1] = lrui[i] * (z - x[i]);
    repb(i,n) rrui[i] = rrui[i+1] * (z - x[i]);
    vector<mint> dxs(n,1);
    rep(i,n) rep(j,n){
        if (i == j) continue;
        dxs[i] *= x[i] - x[j];
    }
    rep(i,n) dxs[i] = mint(1) / dxs[i];
    mint a = 0, b = 0, c = 0;
    rep(i,n) a += y[i] * lrui[i] * rrui[i+1] * dxs[i];
    a *= n;
    rep(i,n) b += y[i] * dxs[i];
    rep(i,n) c += lrui[i] * rrui[i+1];
    mint ans = a - b * c;
    cout << ans.val() << endl;
}