//GOD PLEASE HELP ME ,GOD PLEASE HELP ME , GOD PLEASE HELP ME
//Name Rishiraj Kalita
// sc id : 1912041

#include<bits/stdc++.h>
using namespace std;
#define gc getchar_unlocked
#define fo(i,n) for(i=0;i<n;i++)
#define Fo(i,k,n) for(i=k;k<n?i<n:i>n;k<n?i+=1:i-=1)
#define ll long long
#define si(x)    scanf("%d",&x)
#define sl(x)    scanf("%lld",&x)
#define ss(s)    scanf("%s",s)
#define pi(x)    printf("%d\n",x)
#define pl(x)    printf("%lld\n",x)
#define ps(s)    printf("%s\n",s)
#define deb(x) cout << #x << "=" << x << endl
#define deb2(x, y) cout << #x << "=" << x << "," << #y << "=" << y << endl
#define deb3(x, y, z) cout << #x << "=" << x << "," << #y << "=" << y <<","<< #z << "=" << z << endl
#define debv(v) for(auto x:v) cout<<x<<" "
#define debg(g,n) for(int i=1;i<=n;i++){cout<<i<<"--->";for(auto x:g[i]){cout<<x<<" ";}cout<<"\n";}
#define clrg(g,n) for(int i=0;i<=n;i++) g[i].clear();
#define pb push_back
#define mp make_pair
#define MinHeap priority_queue <ll, vector<ll>, greater<ll> >
#define e endl
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof(x))
#define sortall(x) sort(all(x))
#define tr(it, a) for(auto it = a.begin(); it != a.end(); it++)
#define PI 3.1415926535897932384626
#define inf 9000000000000000000
typedef pair<int, int>    pii;
typedef pair<ll, ll>    pl;
typedef vector<int>        vi;
typedef vector<ll>        vl;
typedef vector<pii>        vpii;
typedef vector<pl>        vpl;
typedef vector<vi>        vvi;
typedef vector<vl>        vvl;
mt19937_64 rang(chrono::high_resolution_clock::now().time_since_epoch().count());
int rng(int lim) {
    uniform_int_distribution<int> uid(0,lim-1);
    return uid(rang);
}
int mpow(int base, int exp);
void ipgraph(int n, int m);
void dfs(int u, int par);

const int mod = 1000000007;
const int N = 3e5, M = N;
//=======================

vi g[N];
int a[N];

void solve() {
    ll i, j, n,k,data,m,f=1;
    ll a,b,c,d;
    cin>>a>>b>>c>>d;
    if(d*c-b<=0)
    {
        cout<<"-1\n";
        return;
    }
    data=d*c-b;
    if(a%(data)==0)
    {
        cout<<a/data;
    }
    else{
        cout<<a/data+1;
    }

  }

int main() {
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    srand(chrono::high_resolution_clock::now().time_since_epoch().count());

    int t = 1;
    //cin >> t;
    while(t--) {
      solve();
    }

    return 0;
}

int mpow(int base, int exp) {
  base %= mod;
  int result = 1;
  while (exp > 0) {
    if (exp & 1) result = ((ll)result * base) % mod;
    base = ((ll)base * base) % mod;
    exp >>= 1;
  }
  return result;
}

void ipgraph(int n, int m){
    int i, u, v;
    while(m--){
        cin>>u>>v;
   // u--, v--;
        g[u].pb(v);
        g[v].pb(u);
    }
}

void dfs(int u, int par){
    for(int v:g[u]){
        if (v == par) continue;
        dfs(v, u);
    }
}





#include<bits/stdc++.h>
using namespace std;
#define ll long long

void solve(){
    ll a,b,c,d;
    cin>>a>>b>>c>>d;
    ll temp=(a);
    ll temp1=(d*c-b);
    if(temp1<=0)
          cout<<-1<<endl;
    else{
    if(temp%temp1==0)
    cout<<temp/temp1<<endl;
    else
        cout<<temp/temp1+1<<endl;
    }

}
int main(){
  ll t=1;
  //cin>>t;
  while(t--){
    solve();
  }
}
