#include<bits/stdc++.h>
#define _ int
#define _____ 114514
#define ______ main
#define _______ scanf
#define ________ printf
#define __________ for
#define ______________ if
#define _______________ return
#define __________________ max
#define ___________________ using namespace std
___________________;
_ __,___,____,____________[_____],_____________,________________,_________________;
_ ______(){
    _______("%d",&__);
    __________(_ ___________;___________<=__;___________++){
        _______("%d",&____________[___________]);
    }
    _______("%d%d",&___,&____);
    __________(_ ___________;___________<=__;___________++){
        _____________+=____________[___________];
    }
    ______________(_____________<__*___||_____________>__*____){
        ________("-1");
        _______________ 0;
    } 
    __________(_ ___________;___________<=__;___________++){
        ______________(____________[___________]<1){
            ________________+=___-____________[___________];
        }
        ______________(____________[___________]>____){
            _________________+=____________[___________]-____;
        }
    }
    ________("%d",__________________(________________,_________________));
    _______________ 0;
}