Example

Input

100 1 0
50 100


Output

14.57738
#include <bits/stdc++.h>

using namespace std;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
template<class T> inline T sqr(T x) {return x*x;}

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a)  (a).begin(),(a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define exist(s,e) ((s).find(e)!=(s).end())
#define range(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)  range(i,0,n)
#define clr(a,b) memset((a), (b) ,sizeof(a))
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi  = acos(-1.0);
const ll INF =1LL << 62;
const int inf =1 << 29;

int d,n,b;
int p[15];
int h[15];
 
double y(double x,double vx,double vy){
	return -(1.0/2.0/vx/vx)*x*x+(vy/vx)*x;
}

double check(const double unit,const double htar){
	const double vx=sqrt(unit*unit/8.0/htar);
	const double vy=unit/2.0/vx;  
	rep(i,n){
		double pos=1.0*p[i];
		int div=pos/unit;
		pos-=div*unit;
		//dump(pos)
		double height=y(pos,vx,vy);
		//dump(height)

		if(abs(pos)<eps)
			return false;

		if(height < h[i])
			return false;
	}
	return true;
}


int main(void){

	cin >> d >> n >> b;
	rep(i,n) cin >> p[i] >> h[i];

	double ans=inf;

	rep(i,b+1){
		const double unit=1.0*d/(i+1);

		double lb=eps,ub=INF;

		rep(loop,200){
			double m=(lb+ub)/2.0;
		//dump(m)
			if(check(unit,m))
				ub=m;
			else
				lb=m;
		}
		double vx=sqrt(unit*unit/8.0/lb);
		double vy=unit/2.0/vx;
		ans=min(ans,sqrt(vx*vx+vy*vy));

		const double t=unit/4.0;
		if(check(unit,t)){
			double vx=sqrt(unit*unit/8.0/t);
			double vy=unit/2.0/vx;
			ans=min(ans,sqrt(vx*vx+vy*vy));
		}
	}
	cout.precision(9);
	cout << fixed;
	cout  << ans << endl;
	return 0;
}