#include<bits/stdc++.h>
using namespace std;
double t,sum;
int n;
struct aa{int m,u; double j;}a[105];
bool cmp(aa am,aa b){ return am.j>b.j;}
int main(){
    cin>>n>>t;
    for(int i=1;i<=n;i++){
        cin>>a[i].m>>a[i].u;
        a[i].j=double(a[i].u/a[i].m);
    }
    sort(a+1,a+1+n,cmp);
    int i=1;
    while(t>0){
        if(t<a[i].m) sum+=t*a[i].j,t=0;
        else sum+=a[i].u,t-=a[i].m;
        i++;
    }
    cout<<fixed<<setprecision(2)<<sum;
    return 0;
}

样例过了，第一个测试点RE其他都是WA求求大神们调一下谢谢