#include using namespace std; using LL = long long; using ULL = unsigned long long; #define rep(i,n) for(int i=0; i<(n); i++) int N; int A[200000]; int X[200000][4]; const int INF = 500000000; int main() { cin >> N; rep(i, N) cin >> A[i]; rep(i, N) rep(j, N) X[i][j] = INF; for (int i = 0; i < N - 1; i++) X[i + 1][0] = min(X[i][0], A[i]); for (int i = N - 1; i >= 1; i--) X[i - 1][1] = min(X[i][1], A[i]); set S; S.insert(INF); for (int i = 0; i < N - 1; i++) { S.insert(A[i]); X[i + 1][2] = *S.upper_bound(A[i + 1]); } S.clear(); S.insert(INF); for (int i = N - 1; i >= 1; i--) { S.insert(A[i]); X[i - 1][3] = *S.upper_bound(A[i - 1]); } int ans = INF; for (int i = 1; i < N - 1; i++) { if (X[i][0] < A[i] && A[i] > X[i][1]) ans = min(ans, X[i][0] + A[i] + X[i][1]); if (X[i][2] > A[i] && A[i] < X[i][3]) ans = min(ans, X[i][2] + A[i] + X[i][3]); } cout << (ans == INF ? -1 : ans) << endl; return 0; }