#include <cstdio>

using namespace std;
#define MAX 1000000
int v[MAX+1];
int main()
{
    freopen("operatii.in","r",stdin);
    freopen("operatii.out","w",stdout);
    int n,i,dif;
    long long mis=0;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
      scanf("%d",&v[i]);
    for(i=2;i<=n;i++)
    {
      dif=v[i]-v[i-1];
      if(dif>0)
        mis=mis+dif;
    }
    printf("%lld",mis);
    return 0;
}