class Solution 
{
public:
    
    void solve(vector<int>&arr,int n,int N,int s,int e,int cnt,int &ans)
    {
        if(n<0)
        {
            return;
        }
        if(s<=0 && e>=N)
        {
            ans=min(ans,cnt);
        }
        solve(arr,n-1,N,min(n-arr[n],s),max(n+arr[n],e),cnt+1,ans);
        solve(arr,n-1,N,s,e,cnt,ans);
    }
    
    
    
    int minTaps(int n, vector<int>& arr) 
    {
        int cnt=0;
        int ans=INT_MAX;
        int s=INT_MAX;
        int e=INT_MIN;
        int N=n;
        solve(arr,n,N,s,e,cnt,ans);
        if(ans==INT_MAX)
        {
            return -1;
        }
        return ans;
    }
};