CodeForces

//水题
#include <bits/stdc++.h>
using namespace std;
int main()
{
	int c, v0, v1, a, l;
	while (cin >> c >> v0 >> v1 >> a >> l)
	{
		int day = 0;
		if (v0 >= c)
		{
			cout << 1 << endl;
			continue;
		}
		
		day++; c -= v0;
		int flag = 1;
		while (1)
		{
			c += l;
			v0 += a;
			if (v0 > v1) v0 = v1;
			
			if (v0 >= c)
			{
				flag = 0;
				cout << ++day;
				break;
			}
			c -= v0; day++;
		}
		if (!flag) continue;
		else cout << day << endl;
	}
	return 0;
}