#include<stdio.h>
int v[1000001];
int n,i,nr,max,k,j,min,l;

int main(){

FILE *f=fopen("operatii.in","r");
fscanf(f,"%d",&n);

 for(i=1;i<=n;i++){
    fscanf(f,"%d",&v[i]);
 }

fclose(f);

nr=0;

   while(k!=n){
   min=100001;

   j=1;

     while(v[j]==0&&j<n){
     j++;
     }

   k=j;

       while(v[j]!=0&&j<=n){
       if(v[j]<min&&v[j]!=0)min=v[j];
       j++;
       }
   j--;

     for(i=k;i<=j;i++){
     v[i]-=min;
     }

   nr+=min;
   }


FILE *g=fopen("operatii.out","w");
fprintf(g,"%d",nr);
fclose(g);

return 0;
}