#include<cstdio>
namespace IO {
	char buf[1 << 15], *fs, *ft;
	inline char gc() { return (fs == ft && (ft = (fs = buf) + fread(buf, 1, 1 << 15, stdin), fs == ft)) ? 0 : *fs++; }
	inline int qr() {
		int x = 0, ch = gc();
		while (ch<'0' || ch>'9') { ch = gc(); }
		while (ch >= '0'&&ch <= '9') { x = (x << 1) + (x << 3) + ch - '0';ch = gc(); }
		return x;
	}
}using namespace IO;
using namespace std;
/***********************************************************************************************/
int c, v0, v1, a, p, ans = 0;
int main() {
	freopen("MrBA.in", "r", stdin);
	freopen("MrBA.out", "w", stdout);
	c = qr();v0 = qr();v1 = qr();a = qr();p = qr();
	ans++;c -= v0;
	while (c>0) {
		v0 += a;
		if (v0 > v1)v0 = v1;
		ans++;c -= v0 - p;
	}
	printf("%d", ans);
	return 0;
}