#include<stdio.h>
int main()
{
int c, v0, v1, a, l;
scanf("%d%d%d%d%d", &c, &v0, &v1, &a, &l);
int cnt = 1;
c -= v0;
while (c > 0)
{
if (v0 + a <= v1) // v0 + a con <= v1 thi so trang doc ngay hom sau la v0 + a - l
{
c -= (v0+a-l);
v0 += a;
}
else // v0 + a > v1 thi so trang doc ngay hom sau la v1 - l;
{
c -= (v1-l);
}
cnt++;
}
printf("%d", cnt);
}
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