#include <stdio.h> int main() { int a,b,c,d,e,m; scanf("%d%d%d",&a,&b,&c);//a=n,b=h,c=m//m=a-b*c; e=c%b; if(e==0) d=c/b; else d=c/b+1;//没喝完要加1 m=a-d; printf("%d\n",m); return 0; }