#include <bits/stdc++.h>
using namespace std;
ifstream fin("operatii.in");
ofstream fout("operatii.out");
int v[1000001];
int main()
{int i,j,n,mini,t;
unsigned long long nrs=0;
 fin>>n;
 for(i=1;i<=n;i++)
    fin>>v[i];
 i=1;
  while(v[i]==0&&i<=n)
    i++;
  while(i<=n)
  {
     if(v[i]!=0)
     {j=i+1;mini=v[i];
       while(v[j]!=0&&j<=n)
       {if(v[j]<mini)
          mini=v[j];
        j++;
       }
      nrs=nrs+mini;
      for(t=i;t<=j-1;t++)
         v[t]=v[t]-mini;
     }else
      i++;
 }
 fout<<nrs;

}