import std.algorithm;
import std.array;
import std.ascii;
import std.bigint;
import std.complex;
import std.container;
import std.conv;
import std.functional;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

void readlnTo(T...)(ref T t) {
    auto s = readln().split();
    assert(s.length == t.length);
    foreach(ref ti; t) {
        ti = s[0].to!(typeof(ti));
        s = s[1..$];
    }
}

const real eps = 1e-10;

const long p = 1_000_000_000 + 7;

double R = 6378.1;

int calc(double[] d) {
    auto x1 = [cos(d[0]*PI/180)*cos(d[1]*PI/180), cos(d[0]*PI/180)*sin(d[1]*PI/180), sin(d[0]*PI/180)];
    auto x2 = [cos(d[2]*PI/180)*cos(d[3]*PI/180), cos(d[2]*PI/180)*sin(d[3]*PI/180), sin(d[2]*PI/180)];
    auto dot = zip(x1, x2).map!"a[0]*a[1]".sum;
    return round((R * acos(dot))).to!int;
}

void main(){
    while(true) {
        auto l = readln().chomp();
        if(l == "-1 -1 -1 -1") {
            return;
        }
        auto d = l.split(" ").map!(to!double).array;
        writeln(calc(d));
    }
}