import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
sys.setrecursionlimit(10**7)
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################
n,d = na()
z = [na() for i in range(n)]
z = sorted(z)
ans = 0
s = 0
for i in range(n):
    s-=z[i][0]
    ans = min(ans,s)
    s+=z[i][1]
print(ans)