#include<cstdio>
#include<iostream>
using namespace std;
const int N=10005;
int n;
int a[N];
int flag,l,r,ans;
int read(){
	int num=0,f=1;
	char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-') f=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9'){
		num=num*10+c-'0';
		c=getchar();
	}
	return num*f;
}
int main(){
	n=read();
	for(int i=1;i<=n;i++) a[i]=read();
	for(int i=1;i<=n;i++){
		if(!l){
			if(a[i]>=a[i-1]&&a[i]>a[i+1]){
				l=i;
			}
		}
		else{
			if(a[i]>a[i-1]&&a[i]>=a[i+1]){
				r=i;
				int full=min(a[l],a[r]);
				for(int i=l+1;i<=r-1;i++) ans+=full-a[i];
				for(int i=r;;i++){
					if(a[i+1]==a[i]) r++;
					else break;
				}
				l=r;
			}
		}
	}
	printf("%d",ans);
	return 0;
}