int main(void)
{ int i, m, n, facta, factb, factc; while(scanf("%d %d", &m, &n) != 2 || m < n || n == 0) while(getchar() != '\n'); while(getchar() != '\n');
for(i = facta = 1; i <= m; i++)/* n! */ { facta *= i;/* m 的阶乘 */ if(i == n) /* n 的阶乘 */ factb = facta; if(i == (m - n)) factc = facta;/* (m - n) 的阶乘 */ } printf("(m! - n!)/(m-n)! = %d\n", (facta - factb)/factc); getchar(); return 0;
}