1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <algorithm>
 5 #include <vector>
 6 #include <cmath>
 7 #include <queue>
 8 #include <stack>
 9 #include <map>
10 #include <string>
11 #include <set>
12 using namespace std;
13 typedef long long LL;
14 const int INF = 2e9;
15 const LL LNF = 9e18;
16 const int MOD = 1e9+7;
17 const int MAXN = 1e5+10;
18
19 struct node
20 {
21     int val, pos;
22 };
23 node a[MAXN], dp[MAXN];
24
25 bool ok(node x, node y)
26 {
27     return (x.val-y.val)>=(x.pos-y.pos);
28 }
29
30 int Search(node dp[], int n, node x)
31 {
32     int l = 1, r = n;
33     while(l<=r)
34     {
35         int mid = (l+r)>>1;
36         if(ok(x,dp[mid]))
37             l = mid + 1;
38         else
39             r = mid - 1;
40     }
41     return r;
42 }
43
44 int main()
45 {
46     int n, m;
47     while(scanf("%d", &n)!=EOF)
48     {
49         for(int i = 1; i<=n; i++)
50             scanf("%d",&a[i].val);
51         m = 0;
52         for(int i = 1; i<=n; i++)
53             if(a[i].val>=i)
54                 a[++m].val = a[i].val, a[m].pos = i;
55
56         int len = 0;
57         for(int i = 1; i<=m; i++)
58         {
59             if(i==1||ok(a[i],dp[len]))
60                 dp[++len] = a[i];
61             else
62             {
63                 int pos = Search(dp,len,a[i]);
64                 dp[pos+1] = a[i];
65             }
66         }
67         printf("%d\n", n-len);
68     }
69 }