PCK2016-yo-6.cpp

#include<bits/stdc++.h>
using namespace std;

#define int long long
#define rep(i,n) for(int i=0;i<(n);i++)
#define pb push_back
#define all(v) (v).begin(),(v).end()
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;
#define fi first
#define se second
template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

int n;
int p[5000];
int z[5000];
signed main(){
    while(cin>>n,n){
        rep(i,n)cin>>p[i];

        int ans=1001001001ll;
        for(int t=0;t<=p[0];t++){
            int cost=t;
            memset(z,0,sizeof(z));
            z[0]=t;
            for(int i=1;i<n;i++){
                cost+=(p[i-1]-z[i-1])*2;
                z[i]+=p[i-1]-z[i-1];
                chmin(z[i],p[i]);
            }
            cost+=p[n-1]-z[n-1];
            chmin(ans,cost);
        }
        cout<<ans<<endl;
    }
    return 0;
}