#include<stdio.h>
int j,i,n,nr,max,v[1001102],min;

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);



  for(i=1;i<=n;i++){

    if(v[i]>0){
    max=v[i];
    min=v[i];
      while(v[i]>=v[i+1]&&i<=n){
      i++;
      if(v[i]>max)max=v[i];
      if(v[i]<min)min=v[i];
      }


       if(v[i]!=0){
       j=i+1;
	while(v[j]!=0){
	  if(v[j]<min){
	  min=v[j];}
	v[j]-=min;
	j++;
	}

       }

      nr+=max;
    }
  }

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


return 0;
}