if your program is /tmp/a.out and the input is /tmp/in, you can use the following Python 3 script to plot your output:

from matplotlib.pyplot import *
import subprocess

f = open('/tmp/in')
n = int(f.readline())
p = [[int(i) for i in l.split()] for l in f]
print(p)
out = subprocess.run('/tmp/a.out < /tmp/in', stdout=subprocess.PIPE, shell=True).stdout.decode().strip()
res = [int(s) for s in out.split('\n')[1:]]
print(res)
plot([v[0] for v in p],[v[1] for v in p],'ro')
plot([p[i-1][0] for i in res], [p[i-1][1] for i in res],'b-')
axis('equal'); grid(); show()