#include <iostream>
using namespace std;

int main() {
	// your code goes here
	int v[] = {1, 2, 3, 4, 6, 3, 2, 4, 7, 3, 4, 6, 1, 2, 1};
	int count = 0;
	for (int l=0,r=sizeof(v)/sizeof(v[0]),lM = v[0], rM = v[sizeof(v)/sizeof(v[0])]; 
					l < r; 
					lM = max(lM,v[l]), rM = max(rM,v[r]))
		if(lM >= rM)
			count += rM - v[r--];
		else
			count += lM - v[l++];
	cout << count<<endl;
	return 0;
}