#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <queue>
#include <stack>

#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
typedef long long ll;

using namespace std;


int inputValue(){
    int a;
    cin >> a;
    return a;
};

void inputArray(int * p, int a){
    rep(i, a){
        cin >> p[i];
    }
};

void inputVector(vector<int> * p, int a){
    rep(i, a){
        int input;
        cin >> input;
        p -> push_back(input);
    }
}

template <typename T>
void output(T a, int precision) {
    if(precision > 0){
        cout << setprecision(precision)  << a << "\n";
    }
    else{
        cout << a << "\n";
    }
}

bool isTake(int a, int b, int c){
    if ((a < b && b > c && a != c) || (a > b && b < c && a != c)) {
        return true;
    }
    return false;
}

int main(int argc, const char * argv[]) {
    
    // source code
    int d = inputValue();
    vector<int> H(3);
    rep(i, 3){
        H[i] = inputValue();
    }
    // case -1)
    if ((H[0] == 0 && H[1] == 0) || (H[1] == 0 && H[2] == 0) || (H[0] == 0 && H[2] == 0)) {
        output(-1, 0);
        return 0;
    }
    
    if (d == 0 && !isTake(H[0], H[1], H[2])) {
        output(-1, 0);
        return 0;
    }
    
    // case どれかが0
    if (H[1] == 0) {
        output((H[0] == H[2]) ? 1 : 0, 0);
        return 0;
    }
    
    if (H[0] == 0) {
        int ret = (H[1] > H[2]) ? 0 : (H[2] - H[1]) / d + 1;
        output(ret, 0);
        return 0;
    }
    
    if (H[2] == 0) {
        int ret = (H[1] > H[0]) ? 0 : (H[0] - H[1]) / d + 1;
        output(ret, 0);
        return 0;
    }
    
    if (isTake(H[0], H[1], H[2])) {
        output(0, 0);
        return 0;
    }
    
    int ret = min((H[1] - H[0]) / d + 1, (H[2] - H[1]) / d + 1);
    
    output(ret, 0);
    

    
    return 0;
}