function Main(input) {
	var data = input.split("\n")
	var n = parseInt(data[0]);
    var num = data[1].split(" ").map((n) => parseInt(n, 10));
    num.unshift(num[0])
    num.push(num[n-1])
    var sum = 0;
    
    for(var i=0; i < n; i++){
    	sum += Math.min(num[i],num[i+1]);
    }
    console.log(sum)
}
 
// Don't edit this line!
Main(require("fs").readFileSync("/dev/stdin", "utf8"));