#include <stdio.h>
#include <assert.h>

main(){
	int a, b, i;
	double f = 1;
	printf("a = ");
	scanf("%d", &a);
	assert(a > 0);
	printf("b = ");
	scanf("%d", &b);
	assert((b > 0) && (a >= b));
	(void)getchar();
	for(i = b; i >= 1; i--) {
		f *= (a + i - b) / (double)i;
	}
	printf("bin = %g\n", f);
	(void)getchar();

	return 0;
}