#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

using namespace std;

typedef long long ll;

int const xn=,xm=,mod=1e9+;

int n,m,l[xn],r[xn],f[xm][xm][xm],jc[xm],jcn[xm],sl[xm],sr[xm];

int rd()

{

  int ret=,f=; char ch=getchar();

  while(ch<''||ch>''){if(ch=='-')f=; ch=getchar();}

  while(ch>=''&&ch<='')ret=(ret<<)+(ret<<)+ch-'',ch=getchar();

  return f?ret:-ret;

}

ll pw(ll a,int b)

{

  ll ret=;

  for(;b;b>>=,a=(a*a)%mod)

    if(b&)ret=(ret*a)%mod;

  return ret;

}

void init()

{

  jc[]=;

  for(int i=;i<=m;i++)jc[i]=((ll)jc[i-]*i)%mod;

  jcn[m]=pw(jc[m],mod-);

  for(int i=m-;i>=;i--)jcn[i]=((ll)jcn[i+]*(i+))%mod;

}

int A(int n,int m){return (ll)jc[n]*jcn[n-m]%mod;}//(ll)!!!

void upt(int &x,int y){x+=y; while(x>=mod)x-=mod; while(x<)x+=mod;}

int main()

{

  n=rd(); m=rd(); init();

  for(int i=;i<=n;i++)l[i]=rd(),r[i]=rd(),sl[l[i]]++,sr[m-r[i]+]++;

  for(int i=;i<=m;i++)sr[i]+=sr[i-];

  f[][][]=;

  for(int i=,num=;i<m;i++,num=num+sl[i])//列

    for(int j=max(,sl[i+]-);j<=i-num;j++)//剩余

      for(int k=;k<=min(i,n);k++)//填r

    {

      if(!f[i][j][k])continue;

      if(sl[i+])

        upt(f[i+][j+-sl[i+]][k],(ll)f[i][j][k]*A(j+,sl[i+])%mod);

      //,printf("f[%d][%d][%d]=%d A(%d,%d)=%lld f[%d][%d][%d]=%d\n",i,j,k,f[i][j][k],j+1,sl[i+1],A(j+1,sl[i+1]),i+1,j+1-sl[i+1],k,f[i+1][j+1-sl[i+1]][k]);//l

      else upt(f[i+][j+][k],f[i][j][k]);//

      if(sr[i+]>k&&j>=sl[i+])

        upt(f[i+][j-sl[i+]][k+],(ll)f[i][j][k]*A(j,sl[i+])%mod*(sr[i+]-k)%mod);

      //,printf("sr=%d k=%d f[%d][%d][%d]=%d f[%d][%d][%d]=%d\n",sr[i+1],k,i,j,k,f[i][j][k],i+1,j-sl[i+1],k+1,f[i+1][j-sl[i+1]][k+1]);//r(+l)

      if(num-sr[i+]&&j>=sl[i+])

        upt(f[i+][j-sl[i+]][k],(ll)f[i][j][k]*A(j,sl[i+])%mod*(num-sr[i+])%mod);

      //,printf("!l!r:f[%d][%d][%d]=%d A=%lld k=%d f[%d][%d][%d]=%d\n",i,j,k,f[i][j][k],A(j,sl[i+1]),num-sr[i+1],i+1,j-sl[i+1],k,f[i+1][j-sl[i+1]][k]);//!l,!r (+l)

      //            printf("f[%d][%d][%d]=%d\n",i,j,k,f[i][j][k]);

    }

  int ans=;

  for(int j=;j<=m-*n;j++)upt(ans,f[m][j][n]);

  //,printf("f[%d][%d][%d]=%d\n",m,j,n,f[m][j][n]);

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

  return ;

}