#include <iostream>
using namespace std;
int N,ar[110],Cnt;
int main()
{
cin>>N;
for(int x=1; x<=N; x++)cin>>ar[x];
for(int x=1; x<=N; x++)
{
for(int y=1; y<=N; y++)
{
for(int z=y+1; z<=N; z++)
{
if(ar[y]>=ar[z])
{
//cout<<y<<" "<<z<<" "<<ar[y]<<" "<<ar[z]<<endl;
Cnt+=ar[y]-ar[z]+1;
ar[y]=ar[z]-1;
}
}
}
}
cout<<Cnt;
}