函数操作题解

#include<iostream>
#include<string>
using namespace std;
void fish(string& a,string& b,string& c){a=b,b=c,c=b+a;}
string a="4567",b="123",c="1234567";
int main(){
    int n;
    cin>>n;
    while(c.size()<n)fish(a,b,c);
    cout<<c[n-1];
    return 0;
}