// Starcraft 2 enjoyer //
#include <bits/stdc++.h>
// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
using namespace std;
#define LSOne(X) ((X) & -(X))
const int N = 2e6 + 5;
const int M = 1e6 + 5;
const int B = 18;
const long long K = 2;
const int LG = 20;
const int INF = 1e9 + 5;
const int P = 31;
const int MOD = 1e9 + 7;
const int nx[] = {0, 1, 0, -1}, ny[] = {-1, 0, 1, 0};
struct SegmentTree
{
vector<int> mx, mn;
int n;
void update(int v, int val, int pos, int l, int r)
{
if (l == r)
{
mx[v] = val;
mn[v] = val;
}
else
{
int m = (l + r) / 2;
if (pos <= m)
{
update(2 * v, val, pos, l, m);
}
else
{
update(2 * v + 1, val, pos, m + 1, r);
}
mn[v] = min(mn[2 * v], mn[2 * v + 1]);
mx[v] = max(mx[2 * v], mx[2 * v + 1]);
}
}
int getMn(int v, int l, int r, int tl, int tr)
{
if (tl > tr)
return INF;
if (tl <= l && r <= tr)
{
return mn[v];
}
else
{
int m = (l + r) / 2;
return min(getMn(2 * v, l, m, tl, min(tr, m)), getMn(2 * v + 1, m + 1, r, max(tl, m + 1), tr));
}
}
int getMx(int v, int l, int r, int tl, int tr)
{
if (tl > tr)
return -1;
if (tl <= l && r <= tr)
{
return mx[v];
}
else
{
int m = (l + r) / 2;
return max(getMx(2 * v, l, m, tl, min(tr, m)), getMx(2 * v + 1, m + 1, r, max(tl, m + 1), tr));
}
}
SegmentTree(int len)
{
n = len;
mn.assign(4 * n, INF);
mx.assign(4 * n, -1);
}
void update(int val, int pos)
{
update(1, val, pos, 0, n - 1);
}
int getMn(int l, int r)
{
return getMn(1, 0, n - 1, l, r);
}
int getMx(int l, int r)
{
return getMx(1, 0, n - 1, l, r);
}
};
struct Dsu
{
vector<int> parent, type;
vector<int> size;
Dsu(int n)
{
parent.assign(n + 1, 0);
size.assign(n + 1, 1);
type.assign(n + 1, 0);
for (int x = 0; x < n + 1; x++)
{
parent[x] = x;
}
}
pair<int, int> getParent(int x)
{
if (parent[x] == x)
{
return {x, 0};
}
else
{
pair<int, int> p = getParent(parent[x]);
parent[x] = p.first;
type[x] ^= p.second;
return {parent[x], type[x]};
}
}
void update(int a, int b)
{
a = getParent(a).first;
b = getParent(b).first;
if (a != b)
{
if (size[a] < size[b])
{
swap(a, b);
}
parent[b] = a;
type[b] ^= 1;
size[a] += size[b];
}
}
bool compare(int i, int j)
{
return getParent(i).second == getParent(j).second;
}
bool chkConnect(int i, int j)
{
return getParent(i).first == getParent(j).first;
}
};
int n, nxt[N], lst[N];
pair<int, bool> type[N];
pair<int, int> port[N];
long long ans;
inline void calNxt()
{
SegmentTree st(N);
for (int x = 2 * n; x >= 1; x--)
{
auto [a, b] = port[type[x].first];
// cout << a << " " << b << " " << x << "\n";
if (type[x].second)
{
int i = st.getMn(a, b);
// cout << i << " " << a << "\n";
if (i == INF)
nxt[a] = -1;
else
nxt[a] = i;
st.update(a, a);
}
else
{
st.update(INF, a);
}
}
}
inline void calLst()
{
SegmentTree st(N);
for (int x = 1; x <= 2 * n; x++)
{
auto [a, b] = port[type[x].first];
// cout << a << " " << b << " " << x << "\n";
if (!type[x].second)
{
int i = st.getMx(a, b);
if (i == -1)
lst[a] = -1;
else
lst[a] = i;
st.update(b, b);
}
else
{
st.update(-1, b);
}
}
}
inline void solve()
{
cin >> n;
for (int x = 0; x < n; x++)
{
int a, b;
cin >> a >> b;
type[a] = {x, 0};
type[b] = {x, 1};
port[x] = {a, b};
}
ans = 1;
calNxt();
// cout << "\n";
calLst();
Dsu dsu(2 * n);
for (int x = 1; x <= 2 * n; x++)
{
if (type[x].second)
continue;
if (lst[x] != -1)
{
if (dsu.chkConnect(port[type[lst[x]].first].first, x))
{
if (dsu.compare(port[type[lst[x]].first].first, x))
{
cout << 0 << "\n";
return;
}
}
dsu.update(port[type[lst[x]].first].first, x);
}
if (nxt[x] != -1)
{
if (dsu.chkConnect(port[type[nxt[x]].first].first, x))
{
if (dsu.compare(port[type[nxt[x]].first].first, x))
{
cout << 0 << "\n";
return;
}
}
dsu.update(port[type[nxt[x]].first].first, x);
}
if (lst[x] != -1 && nxt[x] != -1)
{
if (lst[x] > nxt[x])
{
cout << 0 << "\n";
return;
}
}
}
// cout << "\n";
for (int x = 1; x <= 2 * n; x++)
{
if (type[x].second)
continue;
if (dsu.getParent(x).first == x)
{
// cout << x << "\n";
ans *= 2;
ans %= MOD;
}
}
cout << ans << "\n";
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t = 1;
// cin >> t;
for (int x = 1; x <= t; x++)
{
solve();
}
return 0;
}
