#include "bits/stdc++.h"
#include <cmath>
#include <limits>

using namespace std;

#define int long long
#define pb push_back
#define f(i,a,n) for(int i=a ; i<n ; i++)

#define F first
#define S second
#define all(c) (c).begin(),(c).end()
#define sz(v) (int)(v).size()
#define fast ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)
#define ll long long 
#define ld long double 
#define pii pair<int, int> 
#define vi vector<int> 





ld x,y,r;
bool sarkha(ld a, ld b) 
{
    return (a - b) <= std::numeric_limits<long double>::epsilon();
}


bool ander(int X, int Y)
{
	ld Xx = (x - X) * (x - X) + (y - Y) * (y - Y);
	ld Yy = r * r;
	return sarkha(Xx, Yy);
}	

void solve() 
{
	cin >> x >> y >> r;
	int A = 0;
	for(int X = -4e5 ; X <= 4e5 ; X++)
  {
		int LEFT = -1e9;
		int RIght = -1e9;
		int L = -2e6, H = 2e6;
		while(L <= H)
    {
			int Middd = (L + H)/2;
			if(ander(X, Middd))
      {
				H = Middd - 1;
				LEFT = Middd;
			}
			else
      {
				if(Middd < y)
        {
					L = Middd + 1;
				}
				else
        {
					H = Middd - 1;
				}
			}
		}

		L = -2e6, H = 2e6;
		while(L <= H)
    {
			int Middd = (L + H)/2;
			if(ander(X, Middd))
      {
				L = Middd + 1;
				RIght = Middd;
			}
			else
      {
				if(Middd < y)
        {
					L = Middd + 1;
				}
				else
        {
					H = Middd - 1;
				}
			}
		}

		if(LEFT != -1e9)
    {
			A += RIght - LEFT + 1;
		}
	}
	cout << A << "\n";
}

int32_t main() {
    #ifndef ONLINE_JUDGE
      freopen("input.txt","r",stdin);
      freopen("output.txt","w",stdout);
        #endif
    fast;
    int t = 1;
    // cin >> t;
    while (t--)  
    {
      solve();
    }
}
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define in pair<int, int>
#define f first
#define s second
#define pb push_back
#define pob pop_back
#define INF 1e17
#define zero (int)0
#define MX (int)3e5+5
#define fast() ios_base::sync_with_stdio(false); cin.tie(NULL);
const int mod = 1e9+7; //may change to that 99.. number.
signed main()
{
	fast();
	int a, b, c, d;
	cin >> a >> b >> c >> d;
	int x = d*c-b;
	if(x <= 0)
	{
		cout << "-1\n";
		return 0;
	}
	int t = a/x;
	t+=(a%x>0);
	cout << t << "\n";
	return 0;
}