#include<iostream>

#include<cstdio>

#define rg register

#define ll long long

using namespace std;

int read()

{

  int x=,y=;char c;

  c=getchar();

  while(c<''||c>'') {if(c=='-') y=-;c=getchar();}

  while(c>=''&&c<='') {x=(x<<)+(x<<)+c-'';c=getchar();}

  return x*y;

}

int n;

ll ans;

int a[],b[];

int lowbit(int x)

{

  return x&(-x);

}

void add(int x,int k)

{

  for(rg int i=x;i<=n;i+=lowbit(i)) b[i]+=k;

}

ll sum(int x)

{

  ll sum1=;

  for(rg int i=x;i>=;i-=lowbit(i))

    sum1+=b[i];

  return sum1;

}

int minn,l,r;

int main()

{

  freopen("road.in","r",stdin);

  freopen("road.out","w",stdout);

  n=read();minn=;

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

    {

      a[i]=read();

      minn=min(a[i],minn);

      add(i,a[i]-a[i-]);

    }

  ans+=minn;

  add(,-minn);

  if(a[]!=) l=;

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

    {

      int s=sum(i);

      if(s)

    {

      if(l==) {l=i;r=i;minn=s;}

      else {minn=min(minn,s);r=i;}

      if(i!=n) continue ;

    }

      else if(l==) continue;

      ans+=minn;

      add(l,-minn);

      if(r<n) add(r+,minn);

      i=l-;l=;

    }

  printf("%lld",ans);

  return ;

}

#include<iostream>

#include<cstdio>

#define il inline

#define Rg register

#define go(i,a,b) for(Rg int i=a;i<=b;++i)

#define ll long long

using namespace std;

il int read()

{

    Rg int x=,y=;char c=getchar();

    while(c<''||c>''){if(c=='-')y=-;c=getchar();}

    while(c>=''&&c<=''){x=(x<<)+(x<<)+c-'';c=getchar();}

    return x*y;

}

int n,x,y;ll as;

int main()

{

    n=read();

    go(i,,n){y=read();if(y>x)as+=y-x;x=y;}

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

    return ;

}