input = open("energii.in", "r")
output = open("energii.out","w")
toInt = lambda a : [int(a[0]), int(a[1])]
n, w = int(input.readline()), int(input.readline())
cost = [50000001]*(w+1)

for i in range(0,n):
    x = toInt(input.readline().split(" "))
    
    for j in range(w, x[0], -1):
        cost[j] = min(cost[j], cost[j - x[0]] + x[1])
    
    for j in range(1,x[0]+1):
        cost[j] = min(cost[j], x[1])
 
output.write("-1") if cost[w] == 50000001 else output.write(str(cost[w]))

input.close()
output.close()