def getMinimumSum(arr):
    n = len(arr)
    if n < 3:
        return -1

    left_min = [None] * n
    min_so_far = float('inf')

    # Populate left_min
    for j in range(n):
        if min_so_far < arr[j]:
            left_min[j] = min_so_far
        else:
            left_min[j] = None
        if arr[j] < min_so_far:
            min_so_far = arr[j]

    right_min = [None] * n
    min_so_far = float('inf')

    # Populate right_min
    for j in range(n-1, -1, -1):
        if min_so_far < arr[j]:
            right_min[j] = min_so_far
        else:
            right_min[j] = None
        if arr[j] < min_so_far:
            min_so_far = arr[j]

    min_sum = float('inf')
    for j in range(n):
        if left_min[j] is not None and right_min[j] is not None:
            current_sum = left_min[j] + arr[j] + right_min[j]
            if current_sum < min_sum:
                min_sum = current_sum

    return min_sum if min_sum != float('inf') else -1

# Example Usage:
if __name__ == "__main__":
    arr = [3, 4, 5, 1, 2, 3, 1]
    result = getMinimumSum(arr)
    print(result)  # Output: 4