haversine

from math import radians, cos, sin, asin, sqrt

def haversine(lat1, lon1, lat2, lon2):

      R = 6371

      dLat = (lat2 - lat1)
      dLon = (lon2 - lon1)
      lat1 = (lat1)
      lat2 = (lat2)

      a = sin(dLat/2)**2 + cos(lat1)*cos(lat2)*sin(dLon/2)**2
      c = 2*asin(sqrt(a))

      return R * c

# Usage
lon1, lat1 = [float(i) for i in input().split()] # 105.96 10.21
lon2, lat2 = [float(i) for i in input().split()] # 107.17 16.79

print("{:.2f}".format(haversine(lat1, lon1, lat2, lon2)))

'''
105.96 10.21
107.17 16.79
'''