#include<fstream.h>   
int main()   
{   
long long n,i,ok1,nr,ok,a[1000001];   
ifstream f("operatii.in");   
ofstream g("operatii.out");   
f>>n;   
for (i=0;i<=n;i++)   
     f>>a[i];   
ok=0;   
nr=0;   
while (ok=0)   
    {   
    ok1=0;     
    for (i=0;i<=n;i++)   
    if (a[i]!=0){   
             a[i]=a[i]-1;   
             ok1=1;   
             if (a[i+1]==0)break;   
            }   
        nr=nr+1;   
        ok=1;   
        for (i=0;i<=n;i++)   
            if (a[i]!=0) {   
              ok=ok-1;   
              break;   
             }   
    }
nr=nr-1;   
g<<nr;   
f.close();   
g.close();   
return 0;   
}