smrdi mi kokot

a, b = [int(x) for x in input().split(" ")]
ludia = [([]) for x in range(0, a)]
for i in range(0, a):
    temp = input().split(" ")
    ludia[i].append(temp[0])
    ludia[i].append(temp[1])
    ludia[i][1] = int(ludia[i][1])
dll = 0
for i in range(0, a):
    if i >= (a-dll):
        break
    for j in range(1, a):
        if j is not i:
            if j >= (a-dll):
                break
            elif ludia[i][0] == ludia[j][0]:
                ludia[i][1] += int(ludia[j][1])
                del ludia[j]
                dll += 1
sup = 0
ludia.sort(key = lambda x: -x[1])
leng = len(ludia)
for i in range(0, b):
    if b >= leng:
        break
    sup += ludia[i][1]
print(sup)