#include <bits/stdc++.h>
#define fst first
#define scd second
#define pb emplace_back
#define mkp make_pair
#define uint unsigned
#define mems(a, x) memset((a), (x), sizeof(a))

using namespace std;
typedef long long ll;
typedef double db;
typedef long double ldb;
typedef unsigned long long ull;
typedef pair<int, int> pii;

inline int read() {
	int x = 0;
	char c = getchar();
	bool f = 0;
	while (c < '0' || c > '9') {
		f |= (c == '-');
		c = getchar();
	}
	while ('0' <= c && c <= '9') {
		x = x * 10 + c - '0';
		c = getchar();
	}
	return f ? -x : x;
}

const int maxn = 200100;
const int N = 200000;
const int B = 447;

ll n, f[maxn], b[maxn];
struct node {
	ll a, h;
} a[maxn];

namespace BLK {
	ll a[maxn], b[maxn], c[maxn];
	int bel[maxn], L[maxn], R[maxn];
	
	inline void init() {
		for (int i = 1; i <= N; ++i) {
			bel[i] = (i - 1) / B + 1;
			if (!L[bel[i]]) {
				L[bel[i]] = i;
			}
			R[bel[i]] = i;
		}
		mems(a, 0x3f);
		mems(b, 0x3f);
		mems(c, 0x3f);
	}
	
	inline void update(int x, ll y) {
		x = N - x + 1;
		a[x] = min(a[x], y);
		int k = bel[x];
		b[L[k]] = a[L[k]];
		for (int i = L[k] + 1; i <= R[k]; ++i) {
			b[i] = min(b[i - 1], a[i]);
		}
		for (int i = k; i <= bel[N]; ++i) {
			c[i] = min(c[i - 1], b[R[i]]);
		}
	}
	
	inline ll query(int x) {
		x = N - x + 1;
		return min(c[bel[x] - 1], b[x]);
	}
}

void solve() {
	n = read() + 1;
	a[1].a = read();
	for (int i = 2; i <= n; ++i) {
		a[i].a = read();
		a[i].h = read();
	}
	sort(a + 1, a + n + 1, [&](const node &a, const node &b) {
		return a.a < b.a;
	});
	for (int i = 1; i <= n; ++i) {
		b[i] = b[i - 1] + max(a[i].h - 1, 0LL) / a[n].a * a[i].a;
	}
	mems(f, 0x3f);
	BLK::init();
	for (int i = 1; i <= n; ++i) {
		if (!a[i].h) {
			f[i] = b[i - 1];
		} else {
			int x = a[i].h - 1;
			int y = sqrt(x);
			for (int j = 1; j <= y; ++j) {
				f[i] = min(f[i], BLK::query(j) + b[i - 1] + a[i].a * (x / j));
			}
			for (int l = y + 1, r; l <= x; l = r + 1) {
				r = x / (x / l);
				f[i] = min(f[i], BLK::query(l) + b[i - 1] + a[i].a * (x / l));
			}
			f[i] = min(f[i], BLK::query(a[i].h) + b[i - 1]);
		}
		if (f[i] < 1e18) {
			BLK::update(a[i].a, f[i] - b[i]);
		}
	}
	ll ans = 9e18;
	for (int i = 1; i <= n; ++i) {
		if (a[i].a == a[n].a) {
			ans = min(ans, f[i] + b[n] - b[i]);
		}
	}
	printf("%lld\n", ans);
}

int main() {
	int T = 1;
	// scanf("%d", &T);
	while (T--) {
		solve();
	}
	return 0;
}