void Solve()
{
this.wr = new Writer(this.isReactive);
//this.wr = new Writer(this.outFilePath);
#if DEBUG
if (!this.isReactive)
{
this.sc = new Scanner(this.inFilePath);
}
else
{
this.sc = new Scanner();
}
#else
this.sc = new Scanner();
#endif
N = sc.NextInt;
t = new int[N].Select(el => sc.NextInt).ToArray();
v = new int[N].Select(el => sc.NextInt).ToArray();
r = new double[N + 1];
for (int i = 1; i < N; i++)
{
r[i] = Math.Min(v[i - 1], v[i]);
}
r[0] = r[N] = 0;
for (int i = 0; i < N; i++)
{
r[i + 1] = Math.Min(r[i + 1], r[i] + t[i]);
}
for (int i = N; i > 0; i--)
{
r[i - 1] = Math.Min(r[i - 1], r[i] + t[i - 1]);
}
double ans = 0;
for (int i = 0; i < N; i++)
{
double buf = 0;
double low = 0, high = t[i];
double ma;
for (int j = 0; j < 100; j++)
{
double mid = (low + high) / 2;
ma = r[i] + mid;
if (ma > v[i])
{
high = mid;
}
else
{
if (ma - (t[i] - mid) <= r[i + 1])
{
low = mid;
}
else
{
high = mid;
}
}
}
double upTime = low;
ma = r[i] + upTime;
double downTime = ma - r[i + 1];
buf = (r[i] + ma) * upTime / 2;
buf += (ma + r[i + 1]) * downTime / 2;
buf += (t[i] - upTime - downTime) * ma;
ans += buf;
}
wr.WriteLine(ans);
}
void MakeTestCase()
{
Random rand = new Random();
this.wr = new Writer(inFilePath);
}