答案

#include<iostream>
using namespace std;
int main(){
int n,x,y;
cin>>n>>x>>y;
   if(y%x>0){
 if(n-y/x-1>=0){
  cout<<n-y/x-1;
 }else{
  cout<<0;
 }
   }else if(n-y/x>=0){
  cout<<n-y/x;
 }else{
  cout<<0;
 }
}