#include <stdio.h>
#define ver(v1,v2)((v1>v2) ? s+=v1-v2 :s+=0 )
long n,i,v1,v2; 
long long s;
int main()
{
    freopen ("operatii.in","r",stdin);
    freopen ("operatii.out","w",stdout);
    scanf("%ld",&n);
    for (i=1;i<=n;i++){
        scanf("%ld ",&v1);
        ver(v1,v2);
        v2=v1;        
        }
    printf("%lld\n",s);
    return 0;
}