n=int(input())
a=[10**12]+list(map(int,input().split()))+[10**12]
s=[]
def ok(i):
    return a[i-1]<a[i] and a[i]>a[i+1]
for i in range(1,n+1):
    if ok(i):s.append(i)
ans=0
while s:
    i=s.pop()
    ans+=1
    a[i]=min(a[i-1],a[i+1])-1
    if ok(i-1):s.append(i-1)
    if ok(i+1):s.append(i+1)
print(ans)