#include<bits/stdc++.h>

using namespace std;

const int mod = 1e9+;

vector<int>v[];

int fa[][],a[],b[],bel[],is[],n,m,vis[];

inline int sf(int wh,int x){return fa[wh][x]==x?x:fa[wh][x]=sf(wh,fa[wh][x]);}

inline void dfs(int x,int f,int d){

    if(vis[x]!=-){

      if(vis[x]!=d){

          puts("");

          exit();

      }

      return;

    }

    vis[x]=d;

    for(int i=;i<v[x].size();i++)

      if(v[x][i]!=f)dfs(v[x][i],x,d^);

}

int main(){

    int i,j,k,Ans=;

    scanf("%d",&n);

    for(i=;i<=*n+;i++)fa[][i]=fa[][i]=i;

    for(i=;i<=n;i++){

      scanf("%d%d",&a[i],&b[i]);

      bel[a[i]]=bel[b[i]]=i;

      is[b[i]]=;

      fa[][b[i]]=b[i]+;

    }

    for(i=;i<=*n;i++)

      if(is[i]){

          int x=a[bel[i]],la=;

          for(j=sf(,x+);j<=i;j=sf(,j+)){

            j=sf(,j);

            v[bel[j]].push_back(bel[i]);

            v[bel[i]].push_back(bel[j]);

            if(la)fa[][la]=j;

            la=j;

        }

        fa[][x]=x+;

      }

    memset(vis,-,sizeof(vis));

    for(i=;i<=n;i++)

      if(vis[i]==-)Ans=Ans*%mod,dfs(i,,);

    cout<<Ans;

    return ;

}