#include<stdio.h>
#define nMAX 1000001
FILE*f;
long n;
long v[nMAX];
long long operatii;
void citeste()
     {
              f=fopen("operatii.in","r");
              fscanf(f,"%d",&n);
              long i;
              for(i=1;i<=n;i++)
                               fscanf(f,"%ld",&v[i]);
              fclose(f);
     }
void rezolvare()
     {
                long i;
                for(i=2;i<n;i++)
                                if(v[i-1]>=v[i])
                                               operatii+=v[i-1]-v[i];
     }
void afisare()
     {
              f=fopen("operatii.out","w");
              fprintf(f,"%lld",operatii);
              fclose(f);
     }
int main ()
     {
          citeste();
          rezolvare();
          afisare();
          return 0;
     }