What is the logic behind this function.?

[vikram_111]

int joseph(int N, int k) {
if(N==1) {
return 1;
}
if(N%2 == 0) {
if(k == 1) {
return 2*joseph(N/2, 1);
} else {
return 2*joseph(N/2, 2) - 1;
}
} else {
if(k == 1) {
return 2*joseph(N/2, 2);
} else {
return 2*joseph(N/2+1, 1) - 1;
}
}
}