#include<bits/stdc++.h>
using namespace std;
int n,a[100100],i,cnt;
int main()
{
    cin>>n;
    for(int i=0; i<n; i++)
        cin>>a[i];
    if(a[i+1]<a[i])
        cnt+=a[i]+a[i]-a[i+1];
    else if(a[i+1]>a[i])
        cnt+=a[i+1]+a[i+1]-a[i];
    cout<<cnt+a[i];
    return 0;
}