#include <bits/stdc++.h>

//Common
using namespace std;using f64 = double;using i64=long long;using u64=unsigned long long;
template<typename T> using Arr=vector<T>;template<typename T> using Func=function<T>;template<typename T> using Str=basic_string<T>;
#define hfor(v, s, e) for(int v=(s);(s)<=v&&v<(e);++v)//half-opened range
#define hfori(v, s, e) for(int v=(e)-1;(s)<=v&&v<(e);--v)//inversion
#define hforo(v, s, e) int v=(s);for(;(s)<=v&&v<(e);++v)//out declaration
#define hforoi(v, s, e) int v=(e)-1; for(;(s)<=v&&v<(e);--v)
#define cfor(v, s, e) hfor(v,(s),(e)+1)//closed range
#define cfori(v, s, e) hfori(v,(s),(e)+1)
#define cforo(v, s, e) hforo(v,(s),(e)+1)
#define cforoi(v, s, e) hforoi(v,(s),(e)+1)
#define rep(v,x) hfor(v,0,(x))
#define repi(v,x) hfori(v,0,(x))
#define repo(v,x) hforo(v,0,(x))
#define all(x) (x).begin(),(x).end()
#define pushb push_back
#define pushf push_front
#define popb pop_back
#define popf pop_front
#define empl emplace
#define emplb emplace_back
#define emplf emplace_front
#define fi first
#define se second
#define mkp make_pair
#define mkt make_tuple
#define cxp constexpr
#define PQMAX(...) std::priority_queue<__VA_ARGS__>
#define PQMIN(...) std::priority_queue<__VA_ARGS__,Arr<__VA_ARGS__>,greater<__VA_ARGS__>>
#define lb lower_bound
#define ub upper_bound

//Math
template<typename T> cxp T inf() { return numeric_limits<T>::max() / 2; }
template<typename T> inline T sq(T x){return x*x;}
cxp int lgc(int x){return 64-__builtin_clzll(x-1);}
cxp int lgf(int x){return 63-__builtin_clzll(x);}
const f64 pi=acosl(-1), eps=1e-10;

//IO
#if !(DEBUG)
	//#pragma GCC optimize ("Ofast")
	auto __PRE_RUN__=(ios::sync_with_stdio(0), cin.tie(0), cout.tie(0),(cout<<fixed<<setprecision(11)), 0);
#endif

//Misc
int sz(const auto& x){return x.size();}
int rd(int lb, int ub){static mt19937 rng(time(0)^i64(new int)); return uniform_int_distribution<int>(lb, ub-1)(rng);}
int rd(int ub=inf<int>()){return rd(0,ub);}
auto split(auto s, auto p){
	Arr<decltype(s)> ret;
	auto it1=s.begin();
	for(auto it2=it1; (it2 = find(it1,s.end(),p)) != s.end(); it1=it2+1)
		ret.pushb({it1, it2});
	ret.pushb({it1,s.end()});
	return ret;
}
template<typename T> T rev(const T& a){return {a.rbegin(),a.rend()};}
Arr<int> range(int n){ Arr<int> ret(n); rep(i,n)ret[i]=i; return ret; }
struct defer{ defer(auto f):f(f){} ~defer(){f();} function<void()> f; };
#define defer(x) auto _##__COUNTER__ = defer([&](){x;});
#define lam(expr, ...) [&](__VA_ARGS__){return expr;}
#define reduce accumulate
template<class... A>
auto ARR(auto n, A&&...a){
	if constexpr(sizeof...(a)==0) return n;
	else return vector(n,ARR(a...));
}
#define XA(name,mn,mx) int& name(int i){\
	static int a[mx-mn+1];\
	return a[i-mn];\
}
#include <sys/stat.h>

#if !(DEBUG)
struct FIO{
	static const int BUF_SZ=1<<24;
	char *p,*q;
	FIO(){
		struct stat z;
		fstat(0, &z);
		setvbuf(stdout, 0, 0, z.st_blksize);
		
		p=new char[BUF_SZ]; q=p+BUF_SZ;
		cin.read(p, BUF_SZ);
	}
	char get(){
		if(p==q) cin.read(p-=BUF_SZ, BUF_SZ);
		return *p++;
	}
	operator bool(){return *p;}

	FIO& operator>>(char& c){
		do{c=get();}while(c==' '||c=='\n');
		return *this;
	}
	template<typename T>
	FIO& operator>>(T& n){
		n=0;
		bool neg = false; 
		int c=get();
		while(c==' '||c=='\n')
			c=get();
		if (c=='-'){
			neg=true;
			c=get();
		}
		while('0'<=c&&c<='9')
			n=n*10+c-'0', c=get();
		if(neg)
			n *= -1;
		return *this;
	}
	FIO& operator>>(string& s){
		int c=get();
		while(c==' '||c=='\n')
			c=get();
		while(c&&c!=' '&&c!='\n'){
			s.pushb(c);
			c=get();
		}
		return *this;
	}
}fcin;
#define cin fcin
#endif

#define endl '\n'//Interactive? Partial Score?
#define int i64//MLE?
using pint = pair<int,int>;
using tint = tuple<int,int,int>;
template<typename T>ostream& operator<<(ostream& s, const Arr<T>& a) {for(auto i:a) cout<<i<<' '; return s;}
auto cinint(){int x;cin>>x;return x;}
auto cinchr(){char x;cin>>x;return x;}
auto cinints(int n){Arr<int> a(n);for(auto&i:a)cin>>i;return a;}

signed main(){
	int n; cin>>n;
	auto a=cinints(n);
	int ph=0;
	int ans=0;
	hfor(i,1,n){
		ph=max(0ll,(ph+a[i-1])-a[i]);
		ans+=ph;
	}
	cout<<ans<<endl;
}


Measured memory_bytes: 6740