题解

这是代码：

#include <cstdio>
#include <string>
int main(){
    std::string a = "4567", b = "123";
    int n; scanf("%d", &n);
    while (b.size() < n){
        std::string c = b + a;
        a = b;
        b = c;
    }
    printf("%c", b[n - 1]);
    return