#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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