"use strict"
let input = require("fs").readFileSync("/dev/stdin", "utf8");
input = input.split('\n');
let N = input.shift();
let Nums = input[0].split(' ').map(x=> x*1);
let ans = Nums[0]+Nums[N-2];
for(let i = 0; i < N - 2; i++){
  ans += Math.min(Nums[i],Nums[i+1]);
}   
console.log(ans);