import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.PriorityQueue;

public class Main {

	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		MyInput in = new MyInput(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskX solver = new TaskX();
		solver.solve(1, in, out);
		out.close();
	}

	static int INF = 1 << 30;
	static long LINF = 1L << 55;
	static int MOD = 1000000007;
	static int[] mh4 = { 0, -1, 1, 0 };
	static int[] mw4 = { -1, 0, 0, 1 };
	static int[] mh8 = { -1, -1, -1, 0, 0, 1, 1, 1 };
	static int[] mw8 = { -1, 0, 1, -1, 1, -1, 0, 1 };

	static class TaskX {

		public void solve(int testNumber, MyInput in, PrintWriter out) {

			int n = in.nextInt();
			long H = in.nextLong();
			PriorityQueue<P> pq = new PriorityQueue<>();
			LazySegTree seg = new LazySegTree(n);

			long cur = H, ans = 0;
			for (int i = 0; i < n-1; i++) {
				long d = in.nextLong(), h = in.nextLong();
				pq.add(new P(h, i));

				seg.add(cur, i, i+1, 0, 0, seg.size());

				cur -= d;

				while (cur <= 0) {
					P p = pq.remove();
					long max = seg.max(p.idx, i+1, 0, 0, seg.size());

					if (max + p.h > H) {
						pq.add(new P(H - max, p.idx));
						continue;
					}

					long count = Math.min(-cur / p.h + 1, (H - max) / p.h);
					ans += count;
					cur += count * p.h;

					seg.add(count * p.h, p.idx, i+1, 0, 0, seg.size());
					pq.add(p);
				}
			}

			out.println(ans);

		}

		class P implements Comparable<P> {
			long h;
			int idx;

			public P(long h, int idx) {
				super();
				this.h = h;
				this.idx = idx;
			}
			@Override
			public int compareTo(P o) {
				return -Long.compare(this.h, o.h);
			}
			@Override
			public String toString() {
				return "P [h=" + h + ", idx=" + idx + "]";
			}
		}

		class LazySegTree {
			int n;
			long[] dat;
			long[] lazy;

			public LazySegTree(int n_) {
				int n = 1;
				while (n < n_) {
					n *= 2;
				}

				this.n = n;
				dat = new long[this.n * 2 - 1];
				lazy = new long[this.n * 2 - 1];
				for (int i = 0; i < this.n * 2 - 1; i++) {
					dat[i] = 0;
					lazy[i] = 0;
				}
			}

			public void update_node(int k) {
				dat[k] = dat[2 * k + 1] + dat[2 * k + 2];
			}

			long max(int a, int b, int k, int l, int r) {
				if (b <= l || r <= a) {
					return 0;
				} else if (a <= l && r <= b) {
					return dat[k] + lazy[k];
				}

				long lch = max(a, b, k * 2 + 1, l, (l + r) / 2);
				long rch = max(a, b, k * 2 + 2, (l + r) / 2, r);

				return (Math.max(lch, rch) + lazy[k]);
			}

			void add(long x, int a, int b, int k, int l, int r) {
				if (b <= l || r <= a)
					return;

				if (a <= l && r <= b) {
					lazy[k] += x;
					while (k > 0) {
						k = (k - 1) / 2;
						dat[k] = Math.max(dat[k * 2 + 1] + lazy[k * 2 + 1],
								dat[k * 2 + 2] + lazy[k * 2 + 2]);
					}
				} else {
					add(x, a, b, k * 2 + 1, l, (l + r) / 2);
					add(x, a, b, k * 2 + 2, (l + r) / 2, r);
				}
			}

			public int size() {
				return this.n;
			}

			public String toString() {
				return Arrays.toString(dat) + "\n" + Arrays.toString(lazy);
			}
		}

	}

	static class MyInput {
		private final BufferedReader in;
		private static int pos;
		private static int readLen;
		private static final char[] buffer = new char[1024 * 8];
		private static char[] str = new char[500 * 8 * 2];
		private static boolean[] isDigit = new boolean[256];
		private static boolean[] isSpace = new boolean[256];
		private static boolean[] isLineSep = new boolean[256];

		static {
			for (int i = 0; i < 10; i++) {
				isDigit['0' + i] = true;
			}
			isDigit['-'] = true;
			isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true;
			isLineSep['\r'] = isLineSep['\n'] = true;
		}

		public MyInput(InputStream is) {
			in = new BufferedReader(new InputStreamReader(is));
		}

		public int read() {
			if (pos >= readLen) {
				pos = 0;
				try {
					readLen = in.read(buffer);
				} catch (IOException e) {
					throw new RuntimeException();
				}
				if (readLen <= 0) {
					throw new MyInput.EndOfFileRuntimeException();
				}
			}
			return buffer[pos++];
		}

		public int nextInt() {
			int len = 0;
			str[len++] = nextChar();
			len = reads(len, isSpace);
			int i = 0;
			int ret = 0;
			if (str[0] == '-') {
				i = 1;
			}
			for (; i < len; i++)
				ret = ret * 10 + str[i] - '0';
			if (str[0] == '-') {
				ret = -ret;
			}
			return ret;
		}

		public long nextLong() {
			int len = 0;
			str[len++] = nextChar();
			len = reads(len, isSpace);
			int i = 0;
			long ret = 0;
			if (str[0] == '-') {
				i = 1;
			}
			for (; i < len; i++)
				ret = ret * 10 + str[i] - '0';
			if (str[0] == '-') {
				ret = -ret;
			}
			return ret;
		}

		public char nextChar() {
			while (true) {
				final int c = read();
				if (!isSpace[c]) {
					return (char) c;
				}
			}
		}

		public String nextString() {
			return new String(nextChars());
		}

		public char[] nextChars() {
			int len = 0;
			str[len++] = nextChar();
			len = reads(len, isSpace);
			return Arrays.copyOf(str, len);
		}

		public char[][] next2DChars(int h, int w) {
			char[][] s = new char[h][w];
			for (int i = 0; i < h; i++) {
				s[i] = nextChars();
			}
			return s;
		}

		int reads(int len, boolean[] accept) {
			try {
				while (true) {
					final int c = read();
					if (accept[c]) {
						break;
					}
					if (str.length == len) {
						char[] rep = new char[str.length * 3 / 2];
						System.arraycopy(str, 0, rep, 0, str.length);
						str = rep;
					}
					str[len++] = (char) c;
				}
			} catch (MyInput.EndOfFileRuntimeException e) {
			}
			return len;
		}

		public int[] nextIntArray(final int n) {
			final int[] res = new int[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextInt();
			}
			return res;
		}

		public int[] nextIntArray1Index(final int n) {
			final int[] res = new int[n + 1];
			for (int i = 1; i < n + 1; i++) {
				res[i] = nextInt();
			}
			return res;
		}

		public int[] nextIntArrayDec(final int n) {
			final int[] res = new int[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextInt() - 1;
			}
			return res;
		}

		public long[] nextLongArray(final int n) {
			final long[] res = new long[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextLong();
			}
			return res;
		}

		public long[] nextLongArray1Index(final int n) {
			final long[] res = new long[n + 1];
			for (int i = 1; i < n + 1; i++) {
				res[i] = nextLong();
			}
			return res;
		}

		public long[] nextLongArrayDec(final int n) {
			final long[] res = new long[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextLong() - 1;
			}
			return res;
		}

		public double nextDouble() {
			return Double.parseDouble(nextString());
		}

		public double[] nextDoubleArray(int n) {
			double[] res = new double[n];
			for (int i = 0; i < n; i++) {
				res[i] = nextDouble();
			}
			return res;
		}

		static class EndOfFileRuntimeException extends RuntimeException {
		}

	}

}



Measured memory_bytes: 50684