#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <array>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

const int INF = INT_MAX / 2;

int longestIncreasingSubsequence(const vector<int>& a)
{
    int n = a.size();
    vector<int> dp(n, INT_MAX);
    for(int i=0; i<n; ++i){
        vector<int>::iterator it = upper_bound(dp.begin(), dp.end(), a[i]);
        *it = a[i];
    }
    return lower_bound(dp.begin(), dp.end(), INT_MAX) - dp.begin();
}

int main()
{
    int n;
    cin >> n;
    vector<int> a(n);
    for(int i=0; i<n; ++i){
        cin >> a[i];
        a[i] -= i;
        if(a[i] <= 0)
            a[i] = -INF - i;
    }

    int ans = n - longestIncreasingSubsequence(a);
    cout << ans << endl;

    return 0;
}