#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define all(x) (x).begin(),(x).end()
//#pragma GCC optimize ("-O3")
using namespace std;
void _main(); int main() { cin.tie(0); ios::sync_with_stdio(false); _main(); }
typedef long long ll; const int inf = INT_MAX / 2; const ll infl = 1LL << 60;
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
//---------------------------------------------------------------------------------------------------
/*---------------------------------------------------------------------------------------------------
　　　　　　　　　　　 ∧＿∧
　　　　　 ∧＿∧ 　（´<_｀ ）　 Welcome to My Coding Space!
　　　　 （ ´_ゝ`）　/　 ⌒i     @hamayanhamayan0
　　　　／　　　＼　 　  |　|
　　　 /　　 /￣￣￣￣/　　|
　 ＿_(__ﾆつ/　    ＿/ .| .|＿＿＿＿
　 　　　＼/＿＿＿＿/　（u　⊃
---------------------------------------------------------------------------------------------------*/












double R, X, Y;
//---------------------------------------------------------------------------------------------------
void _main() {
	cin >> R >> X >> Y;

	double distance = sqrt(X * X + Y * Y);
	int ans = ceil(distance / R);
	if (ans == 1 && distance != R) ans++;

	cout << ans << endl;
}






#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <utility>
using ll = long long;
//#define rep(i, n) for(int i = 0; i < (int)(n); i++)

#define rep(i, n) for(ll i = 0; i < (ll)(n); i++)
using namespace std;


ll n;
ll sum = 0;
ll m;
ll k;
ll minV;

int main() {
    vector<ll> v;
    cin >> n >> m;
    rep(i,m) {
    	cin >> k;
    	v.push_back(k);
    }
    if (m == 0) {
        cout << 1;

    	return 0;
    }

    sort(v.begin(), v.end());
    if(v[v.size()-1] != n) v.push_back(n+1);

    minV = 1000001000;
    if (v[0] - 1 < minV && v[0] != 1) minV = v[0] - 1;
    for (int i = 1; i < v.size(); i++)
    {
        if (v[i] - v[i-1] -1 < minV && (v[i] - v[i-1] -1) != 0) minV = v[i] - v[i-1] -1;
    }
    if (v[0] != 0){
        if ((v[0] - 1) % minV == 0){
        	sum += (v[0] - 1) / minV;
        }
        else{
        	sum += (v[0] - 1) / minV + 1;
        }
    }

    if (minV == 1000001000) {
        cout << 0;

    	return 0;
    }
    for (int i = 1; i < v.size(); i++)
    {
        if((v[i] - v[i-1]-1) % minV == 0){
        	sum += (v[i] - v[i-1] -1) / minV;
        }
        else{
        	sum += (v[i] - v[i-1]-1) / minV + 1;
        }
    }

    cout << sum;

	return 0;
}