#include<bits/stdc++.h>
using namespace std;
#define int long long

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);

    int n; cin >> n;
    int a[n + 1];
    for(int i = 1; i <= n; i++) cin >> a[i];

    int st = -1;
    int en = -1;
    for(int i = n; i > 1; i--) {
        if(a[i] < a[i - 1]) {
            st = i;
            int prev = a[st];
            while(st <= n and a[st] <= prev) {
                prev = a[st];
                st++;
            }
            st--;
            prev = a[st];
            en = st;
            while(en >= 1 and a[en] >= prev) {
                prev = a[en];
                en--;
            }
            en++;
        }
    }
    if(st != -1) {
        int l = en;
        int r = st;
        while(l < r) {
            swap(a[l], a[r]);
            l++;
            r--;
        }
    }
    else {
        st = n; en = n;
    }

    for(int i = 1; i < n; i++) {
        if(a[i] > a[i + 1]) {
            cout << "impossible\n";
            return 0;
        }
    }

    cout << en << " " << st << "\n";

}