Probability of Falling in a Height Range

Ridgeline Coach Works again, same kind of population reference: the measurement is treated as normal with a stated mean and standard deviation.

The berth design has moved on. It is now a fixed-length bunk with a padded headboard, and the comfort tests come back with a lower and an upper limit: taller and your feet press the end, shorter and you slide around in it during braking. Marketing wants the share of people the bunk suits - the ones inside the range, not merely under the top of it. Each layout has its own two limits, and the reference figures change by market.

Task: Print the probability that a randomly chosen person from this population falls between the two limits - the share of the normal model inside those bounds - rounded to 4 decimals.

Input

Four lines: the population mean, the population standard deviation, the lower limit, and the upper limit. All four are decimals; the standard deviation is positive and the upper limit is above the lower.

Output

One line holding the probability, rounded to 4 decimals and printed the way Python prints a float - 0.6827.

Example:

Input:
70
3
67
73

Output:
0.6827