#include using namespace std;

const int MAX_N = 100010; int a[MAX_N], lis[MAX_N];

int main() { int n; cin >> n; for (int i = 0; i < n; ++i) { cin >> a[i]; a[i] -= i; // 转换为非严格递增问题 }

int len = 0;
for (int i = 0; i < n; ++i) {
    // 二分查找第一个大于a[i]的位置
    int left = 0, right = len;
    while (left < right) {
        int mid = (left + right) / 2;
        if (lis[mid] > a[i]) {
            right = mid;
        } else {
            left = mid + 1;
        }
    }
    if (left == len) {
        lis[len++] = a[i];
    } else {
        lis[left] = a[i];
    }
}

cout << n - len << endl;
return 0;

}