#include<stdio.h>

int v[1000005];

int n,i,nr,k,j,min,l;

int main(){



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

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

 fclose(f);

nr=0;


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

  j=i;


     if(v[i]==0)l=i;
     if(v[i]!=0){
      min=v[j];

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

       for(k=i;k<=j-1;k++){

	if(min>v[k])v[k]=0;

	  else v[k]-=min;
       }

     i=l;
     nr+=min;
     }
  }


fprintf(g,"%d",nr);
fclose(g);

return 0;
}