#include <iostream>
#include <vector>
#include <unordered_map>
#include <unordered_set>

using namespace std;

void FindSubarray(const vector<int>& v, int x) {
    int n = v.size();

    vector<int> part_sum_for_idx(n + 1);
    part_sum_for_idx[0] = 0;
    for (int i = 1; i <= n; ++i) {
        part_sum_for_idx[i] = part_sum_for_idx[i - 1] + v[i - 1];
    }

    unordered_map<int, unordered_set<int>> indices_for_ps;
    for (int i = 0; i <= n; ++i) {
        indices_for_ps[part_sum_for_idx[i]].insert(i);
    }

    for (int i = 0; i <= n; ++i) {
        int required_ps = part_sum_for_idx[i] + x;
        indices_for_ps[part_sum_for_idx[i]].erase(i);
        if (indices_for_ps[part_sum_for_idx[i]].empty()) {
            indices_for_ps.erase(part_sum_for_idx[i]);
        }
        if (indices_for_ps.count(required_ps) != 0) {
            cout << "Subarray from " << i + 1
                << " to " << *(indices_for_ps[required_ps].begin())
                << " is OK!" << endl;
            return;
        }
    }

    cout << "IMPOSSIBLE!" << endl;
}

int main() {
    FindSubarray({2, 1, 1, -1, -2}, 3);
    FindSubarray({1, 2, 3, 4, 5}, -3);
    FindSubarray({1, 2, 3, 4, 5}, 15);
    FindSubarray({-1, -1, -1, 333, -5, +5, 444, -1, -1}, 777);
    FindSubarray({1, -1, 1, -1, 1}, 0);
    FindSubarray({1, -1, 1, -1, 1}, 1);
    FindSubarray({1, -1, 1, -1, 1}, -1);
    FindSubarray({1, -1, 1}, -1);
    FindSubarray({1, -1, 1, -1, 1}, 1);
    FindSubarray({1, -1, 1, -1, 1, -1}, 1);
    FindSubarray({-1, 1, -1, 1, -1, -1}, 1);
    FindSubarray({-1, 1, -1, 1, -1}, 1);
    FindSubarray({1, -1, 1, -1, 1}, 2);
    FindSubarray({-1}, -1);
    FindSubarray({0, -1}, 2);
    return 0;
}