#include<stdio.h>  
    int v[1000000];  
    int main()  
    {  
        long long nr=0,n,rnk=0,nro=0;  
        freopen("operatii.in","r",stdin);  
        freopen("operatii.out","w",stdout);  
        scanf("%lld",&n);  
       int put=1;  
       for(int i=0;i<n;++i)  
       {  
           scanf("%d",v+i);  
           if(!v[i])  
               if(!put)  
                   {  
                       nr+=nro;  
                       put=1;  
                       rnk=0;  
                       nro=0;  
                   }  
           if(v[i])  
               {  
                   if(i)  
                       rnk=v[i-1];  
                  if(v[i]>rnk)  
                     nro+=v[i]-rnk;  
                   put=0;  
               }  
       }  
       if(v[n-1])  
           nr+=nro;  
       printf("%lld",nr);  
         
       return 0;  
   }