#include<bits/stdc++.h>
 
using namespace std;
 
#define ll long long
 
#define itr(i,a,b) for(int i=(int)a;i<(int)b;i++)
 
int main(){
 
    ll n,m; cin>>n>>m;
 
    ll a[n],b[m], sa=0, sb=0, ans=0, j=0;
 
    itr(i,0,n) {cin>>a[i]; sa+=a[i];}
 
    itr(i,0,m) {cin>>b[i]; sb+=b[i];}
 
    sort (b,b+m, greater<>());
 
    while(m){
 
        if(m*(sa+ans)>n*(sb-ans)) break;
 
        ll x=1,k=j;
 
        while(b[k]==b[k+1]){x++;k++; }
 
        ans+=b[j]*x;
 
        n+=x; m-=x; j+=x;
 
    }
 
    cout<<(m? ans:-1);
 
}
 

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MyA0CjUgMSAzIAo4IDUgNCA5

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5 1 3 
8 5 4 9