#include <stdio.h>
long long int a[1000010],n,i,k;
int main ()  
{  
    freopen("operatii.in","r",stdin);  
    freopen("operatii.out","w",stdout);  
    scanf("%lld",&n);  
    for(i=0;i<n;i++)  
        scanf("%lld",&a[i]);  
    k=0;  
    for (i=0;i<n-1;i++)  
        if (a[i+1]>a[i])  
            k=k+(a[i+1]-a[i]);  
    printf ("%lld",k);  
  
    return 0;  
}