过程如下

#include<iostream>
#include<cstring>

using namespace std;

int main(){
int n;
cin >> n;
string a,b,c;
b = "123";
a = "4567";
c = b+a;
while(c.size()<n){

	a = b;
	b = c;
	c = b + a;
}
cout << c[n-1];
return 0;

}