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#include <iostream>
#include <queue>
#include <ranges>
#include <vector>
constexpr size_t inf = 1999999999;
int main() {
size_t n, m;
std::cin >> n >> m;
std::vector<std::vector<size_t>> a(n);
for (size_t i = 0; i < m; i++) {
size_t x, y;
std::cin >> x >> y;
a[x-1].push_back(y-1);
a[y-1].push_back(x-1);
}
std::queue<size_t> q;
std::vector<size_t> d(n, inf);
d[0] = 0;
q.push(0);
while (!q.empty()) {
auto i = q.front();
q.pop();
if (i == n-1) break;
for (auto j : a[i]) {
if (d[j] > d[i]+1) {
d[j] = d[i] + 1;
q.push(j);
}
}
}
if (d[n-1] == inf) {
std::cout << "IMPOSSIBLE\n";
} else {
std::cout << d[n-1]+1 << "\n";
// Backtracking
std::vector<size_t> v;
v.push_back(n-1);
while (v.back() != 0) {
for (auto j : a[v.back()]) {
if (d[j] == d[v.back()]-1) {
v.push_back(j);
break;
}
}
}
for (auto x : v | std::views::reverse)
std::cout << x+1 << " ";
std::cout << "\n";
}
}
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