代码如下

n,b=map(int,input().split())
s=[]
for i in range(n):
    m,v=map(int,input().split())
    s.append((m,v))
s.sort(key=lambda s:v/m,reverse=True)
def n(a,w):
    m=[0 for i in range(len(s))]
    value=0
    for i,(weight,prize) in enumerate(s):
        if w>weight:
            value+=prize
            w-=weight
        else:
            value+=(w/weight)*prize
            w=0
            break
    print("%.2f"%value)
n(s,b)