#include<stdio.h>
#include<vector>
#include<algorithm>
#include<set>
#include<queue>
using namespace std;
#pragma warning (disable: 4996)
#define SIZE (1<<21)
int toz[SIZE];
class segtree
{
public:
int seg1[22][SIZE];
int seg2[22][SIZE];
int low[SIZE * 2], u1[SIZE * 2], u2[SIZE * 2];
int x[SIZE * 2];
int pt;
void init()
{
for (int i = 0; i < SIZE; i++)low[i + SIZE] = u1[i + SIZE] = u2[i + SIZE] = i;
for (int i = SIZE - 1; i >= 1; i--)low[i] = low[i * 2], u1[i] = u1[i * 2], u2[i] = u2[i * 2];
}
void add1(int beg, int end)
{
int node = 1;
int lb = 0, ub = SIZE - 1;
int dep = 0;
for (;;)
{
seg1[dep][u1[node]++] = end;
if (lb == ub)break;
node *= 2;
dep++;
if (beg <= (lb + ub) / 2)ub = (lb + ub) / 2;
else lb = (lb + ub) / 2 + 1, node++;
}
}
void add2(int beg, int end)
{
int node = 1;
int lb = 0, ub = SIZE - 1;
int dep = 0;
for (;;)
{
seg2[dep][u2[node]++] = beg;
if (lb == ub)break;
node *= 2;
dep++;
if (end <= (lb + ub) / 2)ub = (lb + ub) / 2;
else lb = (lb + ub) / 2 + 1, node++;
}
}
void get(int beg, int end, int node, int lb, int ub, int dep)
{
if (end < lb || ub < beg)return;
if (beg <= lb && ub <= end)
{
for (;;)
{
if (low[node] == u1[node])break;
int z = seg1[dep][u1[node] - 1];
if (z <= end)break;
x[pt++] = toz[z];
u1[node]--;
}
for (;;)
{
if (low[node] == u2[node])break;
int z = seg2[dep][u2[node] - 1];
if (z >= beg)break;
x[pt++] = toz[z];
u2[node]--;
}
return;
}
get(beg, end, node * 2, lb, (lb + ub) / 2, dep + 1);
get(beg, end, node * 2 + 1, (lb + ub) / 2 + 1, ub, dep + 1);
}
};
segtree tree;
int a[1000000], b[1000000];
int col[2000000];
typedef pair<int, int>pii;
int main()
{
FILE *in = freopen("in3.txt", "r", stdin);
int num;
scanf("%d", &num);
for (int i = 0; i < num; i++)scanf("%d%d", &a[i], &b[i]), a[i]--, b[i]--, toz[a[i]] = toz[b[i]] = i;
tree.init();
for (int i = 0; i < num + num; i++)if (b[toz[i]] == i)tree.add1(a[toz[i]], b[toz[i]]);
for (int i = num + num - 1; i >= 0; i--)if (a[toz[i]] == i)tree.add2(a[toz[i]], b[toz[i]]);
int ans = 1;
for (int i = 0; i < num; i++)
{
if (col[i] == 0)
{
ans = ans * 2 % 1000000007;
queue<pii>que;
que.push(make_pair(i, 1));
for (;;)
{
if (que.empty())break;
pii z = que.front();
que.pop();
if (col[z.first] != 0)
{
if (col[z.first] != z.second)
{
printf("0\n");
return 0;
}
continue;
}
col[z.first] = z.second;
tree.pt = 0;
tree.get(a[z.first], b[z.first], 1, 0, SIZE - 1, 0);
for (int j = 0; j < tree.pt; j++)que.push(make_pair(tree.x[j], -z.second));
}
}
}
vector<int>va, vb;
for (int i = 0; i < num + num; i++)
{
if (a[toz[i]] == i)
{
if (col[toz[i]] == 1)va.push_back(toz[i]);
else vb.push_back(toz[i]);
}
else
{
if (col[toz[i]] == 1)
{
if (va[va.size() - 1] != toz[i])ans = 0;
else va.pop_back();
}
else
{
if (vb[vb.size() - 1] != toz[i])ans = 0;
else vb.pop_back();
}
}
}
printf("%d\n", ans);
}
