题目传送门

结果

#include<bits/stdc++.h>
using namespace std;
unsigned long long g(unsigned long long i)
{
	if(i==4 || i==9) return 1;
	return 0;
}
unsigned long long e(unsigned long long i)
{
	unsigned long long m=i;
    while(m>0){
        if(m%10==4||m%10==9){
            return 1;
            break;
        }
        else{
            m/=10;
        }
    }
}
int main(){
	unsigned long long n,m,sum=0;;
	cin>>n>>m;
	for(unsigned long long i=n;i<=m;++i)
	{
		if(i<10) {
			if(g(i)) sum++;
		}
		else if(e(i)) sum++;
	}
	cout<<sum<<endl;
}