#include <iostream>
#include <algorithm>
using namespace std;
int main() {
    int n, x;
    cin >> n >> x;

    int niza[n], orginalna[n];
    for(int i = 0; i < n; i++) {
        cin >> niza[i];
        orginalna[i] = niza[i];
    }
    sort(niza, niza + n);
    int i = 0, j = n - 1;

    while(i < j) {
        if(niza[i] + niza[j] == x) {
            for(int k = 0; k < n; k++) {
                if(niza[i] == orginalna[k]) {
                    cout << k + 1 << endl;
                    orginalna[k] = -1;
                    break;
                }
            }
            for(int k = 0; k < n; k++) {
                if(niza[j] == orginalna[k]) {
                    cout << k + 1 << endl;
                    orginalna[k] = -1;
                    break;
                }
            }    
            return 0;
        }
        if(niza[i] + niza[j] < x) {
            i++;
        }
        else {
            j--;
        }
    }

    cout << "IMPOSSIBLE" << endl;
    return 0;
}