long[] store = new long[((int) a+1)/2];
store[0] = 2;
long l = ((int) a)-2;
for (long iy = 0; iy < l; iy++) {
	long ta = store[0];
	store[0]++;

	int ix = 1;
	for (; ix <= (iy+1)/2; ix++) {
		long tb = store[ix];
		store[ix] = ta+tb;
		ta = tb;
	}
	if ((iy & 1) == 0) {
		store[ix] = store[ix-1];
	}
}