题解！！！

#include<bits/stdc++.h>
using namespace std;
int a,b,n,ans,x[40]={0,990,1010,1970,2030,2940,3060,3930,4060,4970,5030,5990,6010,7000},bo[40]; 
void dfs(int k){
	for(int i=1;i<=n+13;i++){
		if(x[i]>=k+a&&x[i]<=k+b&&bo[i]==0){
			if(x[i]==7000){
				ans++;
				return;
			}
			bo[i]=1;
			dfs(x[i]);
			bo[i]=0;
		}
		else if(k+a>=7000){
			ans++;
			return;
		}
	}
	return;
}
int main(){
	cin>>a>>b>>n;
	for(int i=13;i<=n+12;i++) {
        cin>>x[i];
    }
	dfs(0);
	cout<<ans;
	return 0;
}