#include <iostream>
using namespace std;
int main()
{
    int a,b,n,m,t;
    cin>>a>>n>>m>>b>>t;
    int sum=0;
    for(int i=0;i<t;i++)
    {
    	n+=i;
    	if(n>=m)
	    {
	    	sum=a-1;
	    	b++;
	    }
	}
	if(b>=sum)
    {
        	cout<<"YES"<<endl;
	}
	else
	{
		cout<<"NO"<<endl;
	}
	return 0;
 }