#include<stdio.h>

#define INPUT "operatii.in"
#define OUTPUT "operatii.out"
#define DIM 10001

int a[DIM];
int main()
{
    freopen(INPUT,"r",stdin);
    freopen(OUTPUT,"w",stdout);
    int n,i,max=0,j,k=0;
    scanf("%d",&n);
    for(i=1; i<=n; ++i)
    {
             scanf("%d",&a[i]);
             if(a[i]>max)
                         max=a[i];
    }
    while(max>0)
    {
                i=1;
                while(i<=n)
                {
                           if(a[i]==max)
                           {
                                        ++k;
                                        j=i;
                                        while(j<=n&&a[j]==max)
                                        {
                                                              ++j;
                                                              --a[j];
                                        }
                           }
                           ++i;
                }
                --max;
    }
    printf("%d",k-1);
    return 0;
}