// execute g++ main.cpp -std=c++14 -I C:\Users\naoya\Desktop\code\Atcoder
#include<bits/stdc++.h>
//#include<atcoder/all>
typedef long long ll;
typedef long double ld;
using namespace std;
//using namespace atcoder;

using Pii = pair<int, int>;
using Pll = pair<ll, ll>;

//ordered_set 重複不可
#include <ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// use set_function + find_by_order(select itr-num)

#define REP(i, l, n) for(int i=(l), i##_len=(n); i<i##_len; ++i)
#define ALL(x) (x).begin(),(x).end()
#define pb push_back

ll gcd(ll a,ll b){return b ? gcd(b,a%b) : a;}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}

template<class T>inline bool chmax(T &a, T b) {if(a < b) {a = b;return true;}return false;}
template<class T>inline bool chmin(T &a, T b) {if(a > b) {a = b;return true;}return false;}


char alpha[26] = {'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};
char Alpha[26] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};

int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, 1, -1};

//cout << std::fixed << std::setprecision(15) << y << endl; //小数表示

const ll MAX = 3000000; //テーブルの数
const ll MOD = 1e9+7; //mod宣言

long long fac[MAX], finv[MAX], inv[MAX];
// finv ->階乗割り算
// fac ->階乗掛け算

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return (fac[n] * (finv[k] * finv[n - k] % MOD)) % MOD;
}

int main(){
    COMinit();
    ll n, m, k; cin >> n >> m >> k;
    if(n > m + k){
        cout << 0 << endl;
        return 0;
    }
    ll mid = 0;
    cout << (COM(n+m, n) + MOD - COM(n+m, m+k+1)) % MOD << endl;
}
#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using iPair = pair<int,int>;
using lPair = pair<ll, ll>;
using ivector = vector<int>;
using lvector = vector<ll>;
using istack = stack<int>;
using iqueue = queue<int>;
using ivv = vector<vector<int>>;
using lvv = vector<vector<ll>>;

const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3f;
vector<iPair> dir = {{1,0}, {-1,0}, {0,1}, {0,-1}};
#define dump(x) cout << #x << " = " << (x) << endl
#define ALL(x) begin(x),end(x)
#define rep(i,s,e) for(ll i=(ll)(s), i_stop=(ll)(e); i<i_stop; ++i)
#define range(i,s,n) for(ll i=(ll)(s), i_stop=(ll)((s)+(n)); i<i_stop; ++i)
#define foreach(x,container) for(auto &&x:container)
template<typename S, typename T> bool chmax(T& a, S b) {b = (T)b; if(a<b) {a=b;return true;} return false;}
template<typename S, typename T> bool chmin(T& a, S b) {b = (T)b; if(a>b) {a=b;return true;} return false;}
template<typename T> void printArr(vector<T> &arr){
    for(auto &x:arr) {cout << x << " ";} cout << endl;
}

// =====================================================>


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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    solve();
    return 0;
}