'use strict'

const main = input => {
	const args = input.split('\n').map(arg => arg.split(' '))
	const N = parseInt(args[0][0], 10)
	const B = args[1].map(arg => parseInt(arg, 10))
	const A = new Array(N).fill(0)
	let ans = 0

	A[0] = B[0]

	for (let i = 1; i < N - 1; i++) {
		A[i] = Math.min(B[i - 1], B[i])
	}

	A[N - 1] = B[N - 2]

	for (let i = 0; i < N; i++) {
		ans += A[i]
	}

	console.log(ans)
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'))
