'use strict'

function main(input) {
  input = input
    .trim()
    .split('\n')
    .map(v => v.split(' ').map(Number))

  const N = input[0][0]
  const B = input[1]
  // B.push(10e6)
  const A = [...Array(N)].map(v => 0)

  A.push(B[0])
  for (let i = 0; i < N - 2; i++) {
    A[i] = Math.min(B[i], B[i + 1])
  }
  A.push(B[N - 2])
  console.log(A.reduce((a, b) => a + b))
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'))
