#include<bits/stdc++.h>
#include<iostream>
#include<iomanip>
#include<stdio.h>
#include<cstdio>
#include<map>
#include<queue>
#include<stack>
#include<cstring>
#include<algorithm>
#include<cmath> 
#include<cstdlib>
#include<ctime>
#include<string>
#define LL long long
using namespace std;
LL a[10000000];
int main(){
    long long n,i,ans=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++){ 
    	scanf("%d",&a[i]);
    } 
    for(i=2;i<=n;i++){ 
    	ans+=max(a[i],a[i-1]);
    } 
    printf("%d",ans);
    return 0;
}

代码还有错误， 求助