#include <cassert>
#include <utility>
#include <vector>
std::pair<std::vector<int>, long long> transaction(long long M);
void buy_souvenirs(int N, long long P0) {
if (N == 2) {
auto res = transaction(P0 - 1);
return;
}
std::vector<int> have(N); // for each type we want have[i] == i
std::vector<int> a(N); // retreived array
a[0] = P0;
for (int i = 1; i < N; ++i) {
if (have[i] == i) {
continue;
}
auto [got, rem] = transaction(a[i - 1] - 1); // it can either be -1 or -2
if (rem == 0) {
// it was -1, or it could be -2 and the last element is 1
a[i] = a[i - 1] - 1 - (got.size() > 1 and got.back() == N - 1);
} else {
a[i] = a[i - 1] - 2; // it was -2
}
for (int &x : got) {
have[x]++;
}
while (have[i] < i) {
transaction(a[i]);
have[i]++;
}
}
}
