#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], done[N], w[N << 1], p[N << 1];
set <int> nxt;
priority_queue <int> tp[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' << flush;
g[sa].push_back(sb);
g[sb].push_back(sa);
if (sz[a] < sz[b])
swap(a, b);
if (!tp[b].empty() && !tp[a].empty()) {
int tpa = tp[a].top(), tpb = tp[b].top();
if (tpa < tpb)
nxt.erase(-tpa);
else
nxt.erase(-tpb);
}
while (!tp[b].empty()) {
tp[a].push(tp[b].top());
tp[b].pop();
}
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;
for (int i = 1; i <= n; i++) {
f[i] = i, sz[i] = 1;
int a, b;
// cout << i << ": " << flush;
cin >> a >> b;
tp[i].push(a);
p[a] = 0;
p[b] = a;
w[a] = w[b] = i;
}
for (int cur = 1; cur <= m; cur++) {
if (!p[cur]) {
nxt.insert(-cur);
} else {
int nd = - m - 1;
while (!nxt.empty()) {
auto nw = *nxt.upper_bound(nd);
nw *= -1;
if (nw <= p[cur])
break;
dsu(w[nw], w[cur]);
nd = -nw;
}
done[w[cur]] = 1;
int par = father(w[cur]);
if (tp[par].top() == p[cur]) {
nxt.erase(-p[cur]);
tp[par].pop();
}
while (!tp[par].empty() && done[w[tp[par].top()]])
tp[par].pop();
if (!tp[par].empty())
nxt.insert(-tp[par].top());
}
}
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;
}
