#include <iostream>
#include <cmath>
#include <unistd.h>

using namespace std;

int main() {
    int N=21, x0=5, y0=5, s=100, r=4;
    int vx = 1, vy = 5 ;
    char c = 'a';
    for (int t=0; t<=s; t++){
      for (int i=0; i<=N; i++) {
        for (int j=0; j<=N; j++) {
            int d2=(j-x0)*(j-x0)+(i-y0)*(i-y0);
             if (d2<=r*r) {
                cout<< c <<" ";
            }
             else if (i==0 || i==N || j==0 || j==N){
                 cout<<"* ";
             }
            else {
                cout<<"  ";
            }
        }

        cout<<endl;
    }
      x0 += vx;
      y0 += vy;
      if (x0 + r >= N - 1) {
          vx = -vx;
          //int circle_r = x0 + r;
          //int field_r  = N - 1;
          //int d = circle_r - field_r;
          x0 = N - 1 - r;
          //x0 -= d;
      }
      if (y0 + r >= N - 1) {
          vy = -vy;
          //int circle_b = y0 + r;
          //int field_b  = N - 1;
          //int d = circle_b - field_b;
          y0 = N - 1 - r;
          //y0 -= d;
      }
      if (x0 - r <= 0) {
          vx = -vx;
          x0 = r + 1;
          //x0 -= x0 - r - 1;
      }
      if (y0 - r <= 0) {
         vy = -vy;
         //int circle_t = y0 - r;
         //int field_t  = 0;
         //int d = circle_t - field_t;
         y0 = r + 1;
         //y0 -= d - 1;
      }
      c = (c + 1)%10 + 'a';
      cout << "\033[u";
      sleep(1);
  }
    return 0;
}