#define _USE_MATH_DEFINES
#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define MT make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define RT return
#define vv(a,b,c,d) vector<vector<a> >(b,vector<a>(c,d))
#define vvv(a,b,c,d,e) vector<vector<vector<a> > >(b,vv(a,c,d,e))
using ll = long long;
using pii = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;

int longestIncreasingSubsequence(const vector<long long> &a) {
    vector<long long> L(a.size(), LLONG_MAX/2);
    L[0] = a[0];
    int t = 0; // legnth-1
    for (int i = 1; i < (int)a.size(); ++i) if(a[i]>0){
        // 広義(<=), 狭義(<)
        if (L[t] <= a[i])L[++t] = a[i];
        else {
            auto it = lower_bound(L.begin(), L.begin() + t, a[i] + 1);
            if (it != L.end()) *it = a[i];
        }
    }
    return t + 1;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(20);

    int N; cin >> N;
    vll a(N);
    rep(i, N) {
        cin >> a[i];
        a[i] -= i;
    }
    cout << N-longestIncreasingSubsequence(a) << endl;
}