#include <iostream>

using namespace std;

int n;
int a[100];

int ab(int a, int b) {
    if (a > b)
       return a - b;
    else
       return b - a;
}

bool poredu() {
     for (int i = 0; i < n - 1; i++)
         if (a[i] >= a[i + 1])
            return 0;
     return 1;
}

int main() {
    cin>>n;
    for (int i = 0; i < n; i++)
        cin>>a[i];
    
    int koliko = 0;

    while (poredu() == 0) {
    for (int i = 0; i < n - 1; i++)
        if (a[i] >= a[i + 1]) {
                 koliko += ab(a[i], a[i + 1]) + 1;
                 a[i] = a[i] - ab(a[i], a[i + 1]) - 1;                 
        }
}

cout<<koliko<<endl;
           
    
    
    
    int asdf;
    cin>>asdf;
}