#include <bits/stdc++.h>
using namespace std;
#define INF 1<<30
#define endl '\n'
#define maxn 1000005
#define FASTIO ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
typedef long long ll;
const double PI = acos(-1.0);
const ll mod = 1e9 + 7;

inline void normal(ll &a) { a %= mod; (a < 0) && (a += mod); }
inline ll modMul(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a * b) % mod; }
inline ll modAdd(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); return (a + b) % mod; }
inline ll modSub(ll a, ll b) { a %= mod, b %= mod; normal(a), normal(b); a -= b; normal(a); return a; }
inline ll modPow(ll b, ll p) { ll r = 1; while (p) { if (p & 1) r = modMul(r, b); b = modMul(b, b); p >>= 1; } return r; }
inline ll modInverse(ll a) { return modPow(a, mod - 2); }
inline ll modDiv(ll a, ll b) { return modMul(a, modInverse(b)); }


///**
template < typename F, typename S >
ostream& operator << ( ostream& os, const pair< F, S > & p ) {
  return os << "(" << p.first << ", " << p.second << ")";
}

template < typename T >
ostream &operator << ( ostream & os, const vector< T > &v ) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if ( it != v.begin() ) os << ", ";
    os << *it;
  }
  return os << "}";
}

template < typename T >
ostream &operator << ( ostream & os, const set< T > &v ) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if ( it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "]";
}

template < typename F, typename S >
ostream &operator << ( ostream & os, const map< F, S > &v ) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if ( it != v.begin() ) os << ", ";
    os << it -> first << " = " << it -> second ;
  }
  return os << "]";
}

#define dbg(args...) do {cerr << #args << " : "; faltu(args); } while(0)

clock_t tStart = clock();
#define timeStamp dbg("Execution Time: ", (double)(clock() - tStart)/CLOCKS_PER_SEC)

void faltu () { cerr << endl; }

template <typename T>
void faltu( T a[], int n ) {
  for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
  cerr << endl;
}

template <typename T, typename ... hello>
void faltu( T arg, const hello &... rest) { cerr << arg << ' '; faltu(rest...); }
// Program showing a policy-based data structure.
#include <ext/pb_ds/assoc_container.hpp> // Common file 
#include <ext/pb_ds/tree_policy.hpp>
#include <functional> // for less 
#include <iostream>
using namespace __gnu_pbds;
using namespace std;
// GNU link : https://goo.gl/WVDL6g
typedef tree<int, null_type, less_equal<int>, rb_tree_tag,
        tree_order_statistics_node_update>
        new_data_set;

// find_by_order(k) – ফাংশনটি kth ordered element এর একটা পয়েন্টার রিটার্ন করে। অর্থাৎ তুমি চাইলেই kth ইন্ডেক্সে কি আছে, সেটা জেনে ফেলতে পারছো!
// order_of_key(x) – ফাংশনটি x এলিমেন্টটা কোন পজিশনে আছে সেটা বলে দেয়।

//*//**___________________________________________________**/



int main()
{
  FASTIO
  /*
#ifndef ONLINE_JUDGE
  freopen("in.txt", "r", stdin);
  freopen("out.txt", "w", stdout);
  freopen("error.txt", "w", stderr);
#endif
//*/
  int T;
  //scanf("%d", &T);
  T = 1;
  for (int cs = 1; cs <= T; cs++) {
    int n, k, m;
    cin >> n >> k >> m;
    int sm = 0;
    for (int i = 1; i < n; i++) {
      int x;
      cin >> x;
      sm += x;
    }
    for (int i = 0; i <= k; i++) {
      int x = sm + i;
      if (x / n >= m) {
        cout << i << endl;
        return 0;
      }
    }
    cout << -1 << endl;
    return 0;
  }
  return 0;
}
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
#define ls(x) (x << 1)
#define rs(x) (x << 1 | 1)
#define lowbit(x) (x & -x)
const ll INF=0x3f3f3f3f;
const ll LL_INF=0x3f3f3f3f3f3f3f3f;
const double EPS=1e-7;
ll mod=1e9+7;
const ll MOD=998244353;
ll qpow(ll base,ll q){
    ll res=1;
    while(q){
        if(q&1)res=res*base;
        base=base*base;
        q>>=1;
    }
    return res;
}
inline ll read()  
{  ll f=1,x=0;char ch=getchar();
   for(;ch>'9'||ch<'0';ch=getchar())if(ch=='-') f=-1;
   for(;ch<='9'&&ch>='0';ch=getchar())x=x*10+ch-'0';
   return x*f;
}
const int N = 500010;
struct node {
    ll to, t, k, ne;
    bool operator < (const node &a) const{
        return t > a.t;
    }
}e[N];
ll d[N], st[N];
ll n, m, s, y;
ll h[N], idx;
void add(ll x, ll y, ll t, ll k){
    e[++idx] = {y, t, k, h[x]};
    h[x] = idx;
}
ll dijkstra(){
    memset(d, 0x3f, sizeof d);
    priority_queue<node> q;
    d[s] = 0;
    q.push({s, 0});
    while (!q.empty()){
        node t = q.top();
        q.pop();
        ll x = t.to;
        if (st[x]) continue;
        st[x] = 1;
        for (int i = h[x]; i != 0; i = e[i].ne){
            ll to = e[i].to, t = e[i].t, k = e[i].k;
            ll temp = (d[x] + k - 1) / k * k;
            if (d[to] > t + temp){
                d[to] = t + temp;
                q.push({to, d[to]});
            }
        }
    }
    return d[y] == LL_INF ? -1 : d[y];
}
void solve(){
    cin >> n >> m >> s >> y;
    for (int i = 1; i <= m; i++){
        ll a, b, k, t;
        scanf("%lld%lld%lld%lld", &a, &b, &t, &k);
        add(a, b, t, k);
        add(b, a, t, k);
    }
    cout << dijkstra();
}
int main(){   
    int t = 1;
    while (t--) solve();
    return 0;
}