import sys
input=lambda:sys.stdin.readline().rstrip()
T=int(input())
N=list(map(int,input().split()))
M=int(pow(sum(N),0.5))
ans=0
for i in range(M):
	ans+=max(N[i]-i-1,0)
for i in range(M,2*M-1):
	ans+=max(N[i]+i-2*M+1,0)
for i in range(2*M-1,T):
	ans+=N[i]
print(ans)