#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;
}