// D.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <cmath>
#include <algorithm>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

ull h[100000], v[100000];
ll n, H, T;

bool check(ll t)
{
	ll temp = t;
	for (int z = 0; z < T; z++)
	{
		for (int i = n - 1; i >= 0; i--)
		{
			if (h[i] <= t)
				t = max(h[i] - 1, t - v[i]);
		}
		if (t >= H)
			return 1;
		t += temp;
	}
	return 0;
}

int main()
{
	cin >> n >> H >> T;
	ll ans = H;
	for (int i = 0; i < n; i++)
	{
		cin >> h[i] >> v[i];
		//if (h[i] + v[i] >= H && h[i] <= H)
		ans += v[i];
	}
	ll l = 0, r = ans + 1;
	while (l + 1 < r)
	{
		ll m = (l + r) / 2;
		//cout << l << ' ' << r << ' ' << m << ' ' << check(m) << endl;
		//system("pause");
		if (check(m))
			r = m;
		else
			l = m;
	}
	cout << r << endl;
	system("pause");
	return 0;
}

/*
// ConsoleApplication9.cpp : Defines the entry point for the console application.
//

//#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <cmath>
#include <algorithm>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

ull h[100000], v[100000];
ll n, H, T;

bool check(ll t)
{
ll temp = t;
for (int z = 0; z < T; z++)
{
for (int i = n - 1; i >= 0; i--)
{
if (h[i] <= t)
t = max(h[i] - 1, t - v[i]);
}
if (t >= H)
return 1;
t += temp;
}
return 0;
}

int main()
{
//cin >> n >> H >> T;
n = 100000;
H = 1000000000;
T = H;
ll ans = H;
for (int i = 0; i < n; i++)
{
//cin >> h[i] >> v[i];
h[i] = i + 1;
v[i] = H;
//if (h[i] + v[i] >= H && h[i] <= H)
ans += v[i];
}
ll l = 0, r = ans + 1;
while (l + 1 < r)
{
ll m = (l + r) / 2;
//cout << l << ' ' << r << ' ' << m << ' ' << check(m) << endl;
//system("pause");
if (check(m))
r = m;
else
l = m;
}
cout << r << endl;
//system("pause");
return 0;
}


*/