#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define ff first
#define ss second
#define all(s) s.begin(),s.end()
#define rall(s) s.rbegin(),s.rend()
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
ll n;
cin>>n;
ll a[n+5];
for(ll i=1;i<=n;i++){
cin>>a[i];
}
ll ans=1e18;
for(ll i=1;i<=n;i++){
ll l=0,r=0;
for(ll j=1;j<i;j++){
if(a[j]>=a[j+1]){
l+=a[j]-a[j+1]+1;
}
}
for(ll j=i;j<n;j++){
if(a[j]<=a[j+1]){
r+=a[j+1]-a[j]+1;
}
}
ans=min(ans,max(l,r));
}
cout<<ans;
}
