"use strict"

function Main(input) {
  input = input.trim().split('\n');
  const N = Number(input[0].trim());
  const B = input[1].trim().split(' ').map(Number);

  let cnt = N-2;
  let ret = B[0];
  for(let i=0; i<cnt; i++){
    ret += Math.min(B[i], B[i+1])
  }
  ret += B[cnt];
  console.log(ret);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));