N = int(input())
lsp = list(map(int,input().split()))
cnt = 0
for i in range(N):
    v = i+1
    cnt += lsp[i]-v
    for j in range(i+1,N):
        if lsp[j] < lsp[i]:
            lsp[j] += 1
    lsp[i] = v
print(cnt)