#include<bits/stdc++.h> using namespace std; #define ll long long bool is_yes; int digit_sum(ll p){ ll sum=0; while(p>0){ sum+=p%10; p=p/10; } return sum; }

int main() { int T; cin>>T; while(T--){ is_yes=1; ll n; cin>>n; vector a(n+1); for(int i=1;i<=n;i++) { cin>>a[i]; } ll s=0; for(ll i=n-1;i>0;i--) { while(a[i]>a[i+1]) {
if(a[i]<10){ cout<<"-1"<<endl;is_yes=0;break;} a[i]=digit_sum(a[i]); s++; } } if(is_yes){ cout<<s<<endl;} } return 0; }