#include <iostream>
#include <atcoder/modint>

using namespace std;
using namespace atcoder;
using mint = modint998244353;
mint x[10010],y[10010],z[10010],sumL[10010],sumR[10010],dif[10010];
int main(){
    int i,j,n; cin >> n;
    int a; cin >> a; mint X = a;
    for(i=0;i<n;i++){
        int b,c; cin >> b >> c; x[i] = b; y[i] = c;
    }
    for(i=0;i<n;i++){
        dif[i] = 1;
        for(j=0;j<n;j++){
            if(j==i) continue;
            dif[i] *= (x[i] - x[j]);
        }
    }
    sumL[0] = 1;
    for(i=1;i<=n;i++) sumL[i] = sumL[i - 1]*(X - x[i - 1]);
    sumR[n] = 1;
    for(i=n - 1;i>=0;i--) sumR[i] = sumR[i + 1]*(X - x[i]);
    mint ans = 0;
    for(i=0;i<n;i++){
        ans += y[i]*sumL[i]*sumR[i + 1]/dif[i];
        //cout << ans.val() << endl;
    }
    ans *= (mint)(n - 1);
    //cout << ans.val() << endl;
    for(i=0;i<n;i++) z[i] = y[i]/dif[i];
    mint sum = 0;
    for(i=0;i<n;i++) sum += z[i];
    for(i=0;i<n;i++){
        ans -= (sum - z[i])*sumL[i]*sumR[i + 1];
    }
    cout << ans.val() << "\n";
    /*for(i=0;i<n;i++) cout << dif[i].val() << " ";
    cout << endl;
    for(i=0;i<=n;i++) cout << sumL[i].val() << " ";
    cout << endl;
    for(i=0;i<=n;i++) cout << sumR[i].val() << " ";
    cout << endl;*/
}