#include<iostream>
#include<cmath>
using namespace std;
#define REP(i,b,n) for(int i=b;i<n;i++)
#define rep(i,n)   REP(i,0,n)
#define PI acos(-1)
const double R=6378.01;

double dist(double x,double y,double z){
  return sqrt(x*x+y*y+z*z+1e-10);
}

void calc(double  &x,double &y,double &z,
	  double a,double b){
  double phi  = PI/2*a/90.0;
  double theta= PI*b/180.0;
  z=R*sin(phi);
  x=R*cos(phi)*cos(theta);
  y=R*cos(phi)*sin(theta);
}

double solve(double *a){
  double x[2],y[2],z[2];
  rep(i,2){
    calc(x[i],y[i],z[i],
	 a[2*i],a[2*i+1]);
  }
  
  double C=dist(x[0]-x[1],y[0]-y[1],z[0]-z[1]);
  

  double theta = acos((2*R*R-C*C)/(2*R*R));
  if ( !(-2*R*R<=2*R*R-C*C))theta=acos(-1);
  else if ( !(2*R*R-C*C<=2*R*R))theta=acos(1);
  return R*theta;
}

main(){
  double in[4];
  while(cin>>in[0]>>in[1]>>in[2]>>in[3]){
    if ( in[0] == 0 && in[1] == 0 && in[2] == 0 && in[3]==0)break;
    printf("%.0lf\n",solve(in));
  }
}