#include<cstdio>

#include<cmath>

#include<cstdlib>

#include<cstring>

#include<ctime>

#include<algorithm>

#include<queue>

#include<vector>

#include<map>

#define ll long long

#define ull unsigned long long

#define max(a,b) (a>b?a:b)

#define min(a,b) (a<b?a:b)

#define lowbit(x) (x& -x)

#define mod 1000000000

#define inf 0x3f3f3f3f

#define eps 1e-18

#define maxn 510

inline ll read(){ll tmp=; char c=getchar(),f=; for(;c<''||''<c;c=getchar())if(c=='-')f=-; for(;''<=c&&c<='';c=getchar())tmp=(tmp<<)+(tmp<<)+c-''; return tmp*f;}

inline ll power(ll a,ll b){ll ans=; for(;b;b>>=){if(b&)ans=ans*a%mod; a=a*a%mod;} return ans;}

inline ll gcd(ll a,ll b){return b?gcd(b,a%b):a;}

inline void swap(int &a,int &b){int tmp=a; a=b; b=tmp;}

using namespace std;

int st[maxn];

int n,tp;

int main()

{

    n=read();

    ll ans=;

    tp=; st[]=read();

    for(int i=;i<=n;i++){

        int k=read();

        if(tp&&st[tp]<k){

            while(tp&&st[tp]<k)--tp,ans+=st[tp];

            ans+=k-st[tp];

        }

        st[++tp]=k;

    }

    for(int i=;i<tp;i++)

        ans+=st[i];

    printf("%lld\n",ans);

}