#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define ff first
#define ss second
#define all(s) s.begin(),s.end()
#define rall(s) s.rbegin(),s.rend()
int main(){
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
ll n,d;
cin>>n>>d;
ll c[n+5];
for(ll i=1;i<=n;i++){
cin>>c[i];
}
ll q;
cin>>q;
ll a[n+5];
while(q--){
ll l,r;
cin>>l>>r;
for(ll i=l;i<=r;i++){
a[i]=c[i];
}
ll ans=0;
for(ll i=l;i<=r;i++){
ll mn=a[i]%d;
for(ll j=i;j<=r;j++){
a[j]-=mn;
if(a[j]<0){
ans=-1;
break;
}
}
if(ans==-1) break;
}
if(ans==-1){
cout<<ans<<"\n";
continue;
}
for(ll i=l;i<=r;i++){
ll mn=(ll)1e18;
for(ll j=l;j<=r;j++){
mn=min(mn,a[j]);
}
for(ll j=i;j<=r;j++){
a[j]-=mn;
}
ans+=a[i]/d;
}
cout<<ans<<"\n";
}
}
