#!/usr/bin/env python3
import random
def main():
    n = int(input())
    b = list(map(int, input().split()))
    ans = 0
    j = 0
    for i in range(n):
        for _ in range(b[i]):
            ans += abs(j - i)
            j += 1
    print(ans)
if __name__ == "__main__":
    main()