import java.lang.Math.*

fun main(args: Array<String>) {
    val N = readLine()!!.toInt()
    val B = readLine()!!.split(" ").map(String::toInt)

    var rsl = B[0] + B[N-2]
    for (i in 1 until N-1) {
        rsl += min(B[i-1], B[i])
    }

    println(rsl)
}