#include<bits/stdc++.h>
using namespace std;

#define pb push_back
#define mp make_pair 
#define fr first
#define sc second
#define sz(x) x.size()
#define rep(n) for (i = 0; i < n; i++)
#define repc(m,n) for (i = m; i < n; i++)
#define all(v) v.begin(), v.end()
#define min3(a, b, c) min(a, min(b, c))
#define max3(a, b, c) max(a, max(b, c))

#define n_l '\n' 
#define dbg(...) cout << "[" << #__VA_ARGS__ << "]: "; cout << to_string(__VA_ARGS__) << endl
template <typename T, size_t N> int SIZE(const T (&t)[N]){ return N; } template<typename T> int SIZE(const T &t){ return t.size(); } string to_string(const string s, int x1=0, int x2=1e9){ return '"' + ((x1 < s.size()) ? s.substr(x1, x2-x1+1) : "") + '"'; } string to_string(const char* s) { return to_string((string) s); } string to_string(const bool b) { return (b ? "true" : "false"); } string to_string(const char c){ return string({c}); } template<size_t N> string to_string(const bitset<N> &b, int x1=0, int x2=1e9){ string t = ""; for(int __iii__ = min(x1,SIZE(b)),  __jjj__ = min(x2, SIZE(b)-1); __iii__ <= __jjj__; ++__iii__){ t += b[__iii__] + '0'; } return '"' + t + '"'; } template <typename A, typename... C> string to_string(const A (&v), int x1=0, int x2=1e9, C... coords); int l_v_l_v_l = 0, t_a_b_s = 0; template <typename A, typename B> string to_string(const pair<A, B> &p) { l_v_l_v_l++; string res = "(" + to_string(p.first) + ", " + to_string(p.second) + ")"; l_v_l_v_l--; return res; } template <typename A, typename... C> string to_string(const A (&v), int x1, int x2, C... coords) { int rnk = rank<A>::value; string tab(t_a_b_s, ' '); string res = ""; bool first = true; if(l_v_l_v_l == 0) res += n_l; res += tab + "["; x1 = min(x1, SIZE(v)), x2 = min(x2, SIZE(v)); auto l = begin(v); advance(l, x1); auto r = l; advance(r, (x2-x1) + (x2 < SIZE(v))); for (auto e = l; e != r; e = next(e)) { if (!first) { res += ", "; } first = false; l_v_l_v_l++; if(e != l){ if(rnk > 1) { res += n_l; t_a_b_s = l_v_l_v_l; }; } else{ t_a_b_s = 0; } res += to_string(*e, coords...); l_v_l_v_l--; } res += "]"; if(l_v_l_v_l == 0) res += n_l; return res; } void dbgm(){;} template<typename Heads, typename... Tails> void dbgm(Heads H, Tails... T){ cout << to_string(H) << " | "; dbgm(T...); } 
#define dbgm(...) cout << "[" << #__VA_ARGS__ << "]: "; dbgm(__VA_ARGS__); cout << endl

// Some typedef's
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
typedef pair<ll, ll> ii;
typedef vector<ll> vi;
typedef vector<ii> vii;
const double PI = 1.00 * acos(-1.00);

bool sortbysec( pair<ll,ll> a, 
                pair<ll,ll> b) 
{ 
    return (a.second < b.second); 
} 
ll extendgcd(ll a,ll b,ll& x,ll& y)
{
	if(b==0)
	{
		x=1;
		y=0;
		return a;
	}
	ll x1,y1;
	ll gcd = extendgcd(b,a%b,x1,y1);
	x=y1;
	y=x1-y1*(a/b);
	return gcd;
}

void dfs(ll a[],bool vis[],ll pos,ll null,ll neg,ll n)
{
	pos=0;
	null=0;
	neg=0;
	for(ll i=1;i<n;i++)
	{
		if(a[i]-a[i-1]>0)
			pos++;
		else if(a[i]-a[i-1]==0)
			null++;
		else
			neg++;
	}
	if(pos<=n/2 and neg<=n/2)
		return;
	for(ll i=0;i<n;i++)
	{
		if(vis[i])
			continue;
		vis[i]=1;
		dfs(a,vis,pos,null,neg,n);
		if(pos<=n/2 and neg<=n/2)
			break;
		a[i]=-a[i];
		dfs(a,vis,pos,null,neg,n);
		a[i]=-a[i];
		vis[i]=0;
	}
}
vector <ll> prime_fact(ll a)
{
    vector<ll> v;
    while(a%2==0)
    {
        a/=2;
        v.push_back(2);
    }
    for(ll i=3;i<=sqrt(a);i+=2)
    {
        while(a%i==0)
        {
            a/=i;
            v.push_back(i);
        }
    }
    if(a>2)
        v.push_back(a);
    return v;
}
void addEdgeUnd(vector<ll> adj[],ll a,ll b)
{
    adj[a].push_back(b);
    adj[b].push_back(a);
}
void solve()
{
	ll n,m,i,j,k=0,ct=0;
	cin>>n;
	// string s;
	// cin>>s;
	ll mx=INT_MIN;
	ll a[n];
	rep(n)
	cin>>a[i];
	mx=a[0];
	for(i=1;i<n;i++)
	{
		ct+=max(0ll,mx-a[i]);
		mx=max(mx,a[i]);
	}
	cout<<ct;
	
}
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	ll t;
	// cin>>t;
	t=1;
	ll t1=t;
	while(t--)
	{
		// cout<<"Case "<<t1-t<<": ";
		solve();
		cout<<"\n";
	}
	return 0;
}

Measured memory_bytes: 5176