#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int n = ri();
	int a[n];
	for (int i = 0; i < n; i++) a[i] = ri();
	
	std::vector<int> b[n];
	int cnt = 0;
	int64_t res = 0;
	for (int i = 0; i < n; i++)
		for (int j = 0; j < a[i]; j++) res += std::abs(i - cnt++);
	std::cout << res << std::endl;
	return 0;
}