//
//  main.cpp
//  secv
//
//  Created by Eusebiu Rares on 17/09/2020.
//  Copyright © 2020 Eusebiu Rares. All rights reserved.
//

#include <iostream>
#include "fstream"
#include "unordered_map"
#include "vector"
#include "algorithm"

std::fstream input ("secv.in", std::ios::in) ;
std::fstream output ("secv.out", std::ios::out) ;

const int MV = 5000 ;

int v[MV + 1], last ;

void normalise(int n) {
	std::vector<int> temp(n + 1) ;
	std::unordered_map<int, int> resp ;
	for (int i = 1 ; i <= n ; ++ i) {
		temp[i] = v[i] ;
	}
	std::sort(begin(temp), end(temp)) ;
	int var(1) ;
	for (int i = 1 ; i <= n ; ++ i) {
		if (temp[i] != temp[i - 1]) {
			resp[temp[i]] = var ++ ;
		}
	}
	last = var - 1 ;
	for (int i = 1 ; i <= n ; ++ i) {
		v[i] = resp[v[i]] ;
	}
}

int prevPoint[MV + 1] ;
int lastSeen[MV + 1] ;
int sol[MV + 1] ;

int main(int argc, const char * argv[]) {
	int n ; input >> n ;
	if (n == 1) {
		return output << 1, 0 ;
	}
	for (int i = 1 ; i <= n ; ++ i) {
		input >> v[i] ;
	}
	normalise(n) ;
	int ans(1e9) ;
	for (int i = 1 ; i <= n ; ++ i) {
		if (v[i] == 1) {
			prevPoint[i] = i ;
		} else {
			prevPoint[i] = lastSeen[v[i] - 1] ;
		}
		lastSeen[v[i]] = i ;
	}
	for (int i = 1 ; i <= n ; ++ i) {
		if (prevPoint[i]) {
			sol[i] = sol[prevPoint[i]] + (i - prevPoint[i]) ;
		} else {
			sol[i] = 1e9 ;
		}
		if (v[i] == last) {
			ans = std::min(ans, sol[i]) ;
			std::cout << i - sol[i] << ' ' << i << '\n' ;
		}
	}
	if (ans == 1e9) {
		ans = -1 ;
	}
	output << ans + 1 ;
}