</p>

A rectangular cake is transported via a truck to a restaurant. On the way to the destination, the truck hits a pothole, which shatters the cake in N perfectly rectangular pieces of width w_i and length l_i, for 1 ≤ i ≤ N.

At the destination, the damage is assessed, and the customer decides to order a replacement cake of the same dimensions. Unfortunately, the original order form was incompletely filled and only the width W of the cake is known. The restaurant asks for your help to find out the length L of the cake. Fortunately, all pieces of the shattered cake have been kept.

입력 형식

The input consists of the following integers:</p>

• on the first line, the width W of the cake;
• on the second line, the number N of shattered pieces;
• on each of the next N lines, the width w_i and length l_i of each piece.

Limits

• 1 ≤ N ≤ 5 000 000;
• 1 ≤ W, L ≤ 10 000;
• for each 1 ≤ i ≤ N, 1 ≤ w_i, l_i ≤ 10 000.

The output should be the integer L.

예제 입력

4
7
2 3
1 4
1 2
1 2
2 2
2 2
2 1

예제 출력

6