#include <bits/stdc++.h>
using namespace std;
typedef vector<int> vi;
typedef pair<vi, vi> pvv;
vi min_rot(vi v) {
rotate(v.begin(), min_element(v.begin(), v.end()), v.end());
return v;
}
variant<bool, vi> find_journey(int N, int M, vi u, vi v) {
queue<int> s;
vector<set<int>> in(N), out(N);
for (int i = 0; i < M; i++) {
out[u[i]].insert(i);
in[v[i]].insert(i);
}
auto rf = [&](int x) {
if (out[x].empty())
s.push(x);
};
for (int i = 0; i < N; i++)
rf(i);
int q = 0;
vi sf;
while (1) {
auto re = [&](int x) {
for (auto it : in[x]) {
out[u[it]].erase(it);
rf(u[it]);
}
for (auto it : out[x])
in[v[it]].erase(it);
};
for ( ; !s.empty(); s.pop()) {
if (s.front() == q)
return false;
re(s.front());
}
if (out[q].size() == 1) {
int edge = *out[q].begin();
re(q);
q = v[edge];
sf.push_back(edge);
} else {
auto fnd = [&](int x, int e, bool b) {
int y = v[e];
vector<bool> z(N);
vi p = {e};
z[x] = b;
for (; !z[y]; y = v[e]) {
p.push_back(e = *out[y].begin());
z[y] = true;
}
int last = -1;
for (int i = 0; i < (int) p.size(); i++) {
if (x == y)
last = i;
x = v[p[i]];
}
vi t, c;
for (int i = 0; i < (int) p.size(); i++)
if (i < last)
t.push_back(p[i]);
else
c.push_back(p[i]);
return pvv(t, c);
};
auto it = out[q].begin();
pvv c1 = fnd(q, *it++, true), c2 = fnd(q, *it++, false);
vi y;
auto ad = [&](vi &v) {
y.insert(y.end(), v.begin(), v.end());
reverse(v.begin(), v.end());
};
ad(sf);
bool eq = min_rot(c1.second) == min_rot(c2.second);
for (int i = 0; i < 2; i++) {
auto tr = [&](pvv &p1, pvv &p2) {
ad(p1.first);
ad(p1.second);
if (eq)
reverse(p2.second.begin(), p2.second.end());
ad(p1.first);
};
tr(c1, c2);
tr(c2, c1);
}
ad(sf);
return y;
}
}
}
