double f(double lambda1, double lambda2, double phi1, double phi2) {
double r21690404 = lambda1;
double r21690405 = lambda2;
double r21690406 = r21690404 - r21690405;
double r21690407 = sin(r21690406);
double r21690408 = phi2;
double r21690409 = cos(r21690408);
double r21690410 = r21690407 * r21690409;
double r21690411 = phi1;
double r21690412 = cos(r21690411);
double r21690413 = sin(r21690408);
double r21690414 = r21690412 * r21690413;
double r21690415 = sin(r21690411);
double r21690416 = r21690415 * r21690409;
double r21690417 = cos(r21690406);
double r21690418 = r21690416 * r21690417;
double r21690419 = r21690414 - r21690418;
double r21690420 = atan2(r21690410, r21690419);
return r21690420;
}