#include <stdio.h>
#define NM 1000001
long n,v[NM];
int main()
{freopen("operatii.in","r",stdin);
 freopen("operatii.out","w",stdout);
 long long rez=0;
 long i;
 scanf("%ld",&n);
 for(i=1;i<=n;i++) scanf("%ld",&v[i]);
 long max=0;
 for (i=1;i<=n;i++)
    {if(v[i]>max) max=v[i];
     if(v[i]<v[i-1]&&v[i]<v[i+1])
       {rez+=max-v[i];
        max=0;
       }
    }
 rez+=max;
 printf("%lld",rez);
 return 0;
}