题解 | 小红的优惠券

import sys
n,m =map(int,input().split())
p = []
for i in range(m):
    a , b = [int(i) for i in input().split()]
    if n >= a:
        p.append(n-b)
    else:
        pass
if p == []:
    p.append(n)
print(min(p))