求救！急，Compile Error

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<queue>
#include<vector>
#include<set>
using namespace std;
struct mon{
	double num,all,xin;
}a[100]; 
double n,sum,z=0,q=0;
bool cmp(mon a,mon b){ 
	return a.xin>b.xin;
}
int main(){
	cin>>n>>sum;
	for(int i=0;i<n;i++){
		cin>>a[i].num>>a[i].all;
		a[i].xin=a[i].all/a[i].num;
	}
	sort(a+0,a+n,cmp);
	for(int i=0;i<n;i++){
		if(sum-z>a[i].num){
			q+=a[i].all;
			z+=a[i].num;
		}
		else{
			q+=a[i].xin*(a[i].num-sum+z);
			z+=a[i].num-sum+z;
			break;
		}
	}
	printf("%.2lf",q);
	
	return 0;
}