p00375 Celsius and Fahrenheit_28774
In Japan, temperature is usually expressed using the Celsius (℃) scale. In America, they used the Fahrenheit (℉) scale instead. $20$ degrees Celsius is roughly equal to $68$ degrees Fahrenheit. A phrase such as "Today’s temperature is $68$ degrees" is commonly encountered while you are in America.

A value in Fahrenheit can be converted to Celsius by first subtracting $32$ and then multiplying by $\frac{5}{9}$. A simplified method may be used to produce a rough estimate: first subtract $30$ and then divide by $2$. Using the latter method, $68$ Fahrenheit is converted to $19$ Centigrade, i.e., $\frac{(68-30)}{2}$.

Make a program to convert Fahrenheit to Celsius using the simplified method: $C = \frac{F - 30}{2}$.



Input

The input is given in the following format.


$F$


The input line provides a temperature in Fahrenheit $F$ ($30 \leq F \leq 100$), which is an integer divisible by $2$.

Output

Output the converted Celsius temperature in a line.

Examples

Input

68


Output

19


Input

50


Output

10
F = int(input())
print((F-30)/2)

68 50 82 60 116 85 162 51 149 96 238 65 311 558 633 1080 1303 2092 3794 6199 10347 9393 10699 19116 1106 355 642 390 298 57 31 24 104 41 164 319 111 215 192 103 709 1263 1682 864 3288 2981 9202 11734 14312 10436 19258 90 269 350 542 326 10 6 265 607 101 321 291 135 1123 2275 562 246 144 4725 5878 4512 22485 19786 37535 256 159 498 647 39 46 37 114 397 66 000 304 371 71 1684 2835 22 346 7124 8199 6248 11587 8024 54760 54 62 308
19 10 26
 15
 43
 27
 66
 10
 59
 33
 104
 17
 140
 264
 301
 525
 636
 1031
 1882
 3084
 5158
 4681
 5334
 9543
 538
 162
 306
 180
 134
 13
 0
 -3
 37
 5
 67
 144
 40
 92
 81
 36
 339
 616
 826
 417
 1629
 1475
 4586
 5852
 7141
 5203
 9614
 30
 119
 160
 256
 148
 -10
 -12
 117
 288
 35
 145
 130
 52
 546
 1122
 266
 108
 57
 2347
 2924
 2241
 11227
 9878
 18752
 113
 64
 234
 308
 4
 8
 3
 42
 183
 18
 -15
 137
 170
 20
 827
 1402
 -4
 158
 3547
 4084
 3109
 5778
 3997
 27365
 12
 16
 139
