function myout(text){console.log(text);}//standard output
function Main(input) {
	input = input.trim();
	//input = input.trim().split(" ");
	input = input.trim().split("\n");
	//input = input.trim().split(" ").map((a)=>Number(a));
	//input = input.trim().split("\n").map((a)=>Number(a));
  var len = parseInt(input[0]) - 1;
  var b = input[1].split(" ").map((a)=>Number(a));
  var output = b[0] + b[len - 1];
  for(var i = 0; i < len - 1; i++){
    output += Math.min(b[i], b[i + 1]);
  }
  myout(output);
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));
