#include<bits/stdc++.h>

using i64 = long long;
using l64 = long double;

template<typename T>
struct Fenwick {
    int n;
    std::vector<T> a;

    Fenwick(int n_ = 0) {
        init(n_);
    }

    void init(int n_) {
        n = n_;
        a.assign(n + 5, T{});
    }

    void add(int x, const T &v) {
        for (int i = x; i <= n; i += i & -i) {
            a[i] = a[i] + v;
        }
    }

    T sum(int x) {
        T ans{};
        for (int i = x; i > 0; i -= i & -i) {
            ans = ans + a[i];
        }
        return ans;
    }

    T rangeSum(int l, int r) {
        return sum(r) - sum(l);
    }

    int select(const T &k) {
        int x = 0;
        T cur{};
        for (int i = 1 << std::__lg(n); i; i /= 2) {
            if (x + i <= n && cur + a[x + i] <= k) {
                x += i;
                cur = cur + a[x];
            }
        }
        return x;
    }
};

struct Max {
    int a = 0;

    Max operator+(Max x) const {
        return {std::max(a, x.a)};
    }
};

void DAOQI() {
    int n;
    std::cin >> n;
    std::vector<int> a(n + 1);
    std::set<int> se;
    for (int i = 1; i <= n; i++) {
        std::cin >> a[i];
        if (a[i] >= i) {
            se.insert(a[i] - i);
        }
    }

    std::vector<int> d(se.begin(), se.end());
    std::map<int, int> mp;
    for (int i = 0; i < d.size(); i++) {
        mp[d[i]] = i + 1;
    }
    int res = 0;
    Fenwick<Max> fw(d.size());
    for (int i = 1; i <= n; i++) {
        int x = a[i] - i;
        if (!se.count(x)) continue;
        int q = fw.sum(mp[x]).a;
        res = std::max(res, q + 1);
        fw.add(mp[x], {q + 1});
    }
    std::cout << n - res << "\n";
}

signed main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    int T = 1;
    //std::cin >> T;
    while (T--) DAOQI();
    return 0;
}