#include <fstream>
#include <vector>
#include <stdlib.h>
#include <time.h>
using namespace std;
ifstream cin("MrBA.in");
ofstream cout("MrBA.out");
int  c,v0,v1,a,p;
int finish,day;
int cyf()
{	
	cin >> c >> v0 >> v1 >> a >> p;
	c -= v0;
	if(c <= 0)
	{
		cout << 1 << endl;
		cin.close();	
		cout.close();
		return 0;
	}
	//c+=p;
	for (day = 2;c > 0; ++day)
	{
		v0 = min(v0+a,v1);
		
		c -= v0;
		///if(c <= 0)
		//{
		//	break;
		//}
		c+=p;
		
		/* code */
	}
	cout << day-1  << endl;
	cin.close();	
	cout.close();
	return 0;
}
int hhhh = cyf();
int main() {;}