90分WA求助

#include<bits/stdc++.h>
using namespace std;
struct st{
	int a,b,c;
	bool operator <(st &x){
		return a<x.a;
	}
};
int main()
{
	int x,n,i,j=0,ans=0,y;
	cin>>x>>n;
	st a[n];
	for(i=0;i<n;i++)
		cin>>a[i].a>>a[i].b>>a[i].c;
	sort(a,a+n);
	for(i=0;i<n;i++){
		if(a[i].b<=j)
			continue;
		y=a[i].c;
		if(j+y>a[i].b)
			y=a[i].b-j;
		if(j+y>x)
			y=x-j;
		ans+=y*a[i].a;
		j+=y;
	}
	if(j<x)
		cout<<-1;
	else
		cout<<ans;
	return 0; 
 }