#include <bits/stdc++.h>
#define ar array
#define all(x) x.begin(), x.end()
using namespace std;
typedef long long ll;
const int N = 1e6 + 6, mod = 1e9 + 7;
vector <int> g[N];
int f[N], sz[N], d[N];
int father(int x) {
if (f[x] != f[f[x]])
return f[x] = father(f[x]);
return f[x];
}
void dsu(int a, int b) {
int sa = a, sb = b;
a = father(a), b = father(b);
if (a == b)
return;
// cout << sa << ' ' << sb << '\n';
g[sa].push_back(sb);
g[sb].push_back(sa);
if (sz[a] < sz[b])
swap(a, b);
f[b] = a;
sz[a] += sz[b];
}
void dfs(int x, int par) {
d[x] = d[par] + 1;
for (int y : g[x])
if (y != par)
dfs(y, x);
}
int main() {
ios::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int n;
cin >> n;
int m = n << 1;
vector <int> p(m + 1, -1), w(m + 1);
for (int i = 1; i <= n; i++) {
f[i] = i, sz[i] = 1;
int a, b;
// cout << i << ": " << flush;
cin >> a >> b;
p[a] = 0;
p[b] = a;
w[a] = w[b] = i;
}
vector <ar <int, 3>> pos;
int st = -1;
for (int cur = 1; cur <= m; cur++) {
if (!p[cur]) {
int tmp = pos.size();
pos.push_back({cur, st, tmp + 1});
st = tmp;
} else {
int j = st;
while (j >= 0 && pos[j][0] > p[cur]) {
dsu(w[pos[j][0]], w[cur]);
j = pos[j][1];
}
if (j >= 0 && pos[j][0] == p[cur]) {
if (pos[j][1] >= 0)
pos[pos[j][1]][2] = pos[j][2];
if (pos[j][2] < pos.size())
pos[pos[j][2]][1] = pos[j][1];
else if (st == j)
st = pos[j][1];
else
while (true) cout << "something\n" << flush;
j = pos[j][1];
}
int k = j; j = st;
while (j > k) {
int nxt = pos[j][1];
pos[j][1] = k;
pos[j][2] = pos.size();
j = nxt;
}
}
}
int com = 0;
for (int i = 1; i <= n; i++) {
if (!d[i]) {
dfs(i, 0);
com++;
}
}
vector <int> ps[2];
for (int i = 1; i <= m; i++) {
if (!p[i]) {
ps[d[w[i]] & 1].push_back(i);
} else {
int b = d[w[i]] & 1;
if (!ps[b].empty() && ps[b].back() > p[i])
return cout << 0, 0;
ps[b].pop_back();
}
}
int ans = 1;
for (int i = 1; i <= com; i++)
(ans <<= 1) %= mod;
cout << ans;
}
