#include<stdio.h>
#define max(a, b) ((a) > (b) ? (a) : (b))
#define min(a, b) ((a) < (b) ? (a) : (b))
#define max3(a, b, c) ((a) > (max(b, c)) ? (a) : (max(b, c)))
#define min3(a, b, c) ((a) < (min(b, c)) ? (a) : (min(b, c)))
#define MAX 200010
int main(){
	int n, i, A[MAX], lm[MAX], rm[MAX];
	scanf("%d", &n);
	for(i = 0; i < n; ++i) {
		scanf("%d", &A[i]);
	}
	lm[0] = A[0], rm[n - 1] = A[n - 1];
	for(i = 1; i < n; ++i) {
		lm[i] = min(lm[i - 1], A[i]);
		rm[n - i - 1] = min(rm[n - i], A[n - i - 1]);
	}
	int ans = 1e9;
	for(i = 1; i < n - 1; ++i) {
		if(max3(lm[i - 1], A[i], rm[i + 1]) == A[i] || min3(lm[i - 1], A[i], rm[i + 1]) == A[i]) {
			ans = min(ans, lm[i - 1] + A[i] + rm[i + 1]);
		}
	}
	if(ans != 1e9)printf("%d\n", ans);
	else printf("%d\n", -1);
	return 0;
}