function Main(input) {
    input = input.split("\n");
  	var N = Number(input[0]),
        B = input[1].split(' ').map(Number);
  	var sum = B[0] + B[N-2];
  	for(var i=0; i<N-2; i++){
    	sum += Math.min(B[i],B[i+1]);
    }
  console.log(sum);
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"));
