#include<stdio.h>

#include<stdlib.h>

int main(void){

int n,h[100],i,sum=0;

scanf("%d",&n);

for(i=0;i<n;i++){

scanf("%d",&h[i]);}

if(h[0]==0){

sum=sum+h[1];}  

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

if(h[i]==0){

if(h[i-1]<h[i+1]){

sum=sum+h[i-1];}

else{

sum=sum+h[i+1];}

}

}

if(h[n-1]==0){

sum=sum+h[n-2];}

printf("%d",sum);

}