After I tried to use the ptentiometer, I wanted to use other variable resistors. So I bought a flex sensor.
To connect a flex sensor to a breadboar, I soldered wires to a flex sensor. This is my ugly soldering.
I connected a flex sensor to a breadboard insted of a potentiometer.
Green wire is a flex sensor in this picture. I removed a resistor
and I added two more LEDs.
I didn't need to change the program and connection between the arduino and the breadboard.
These are my whole circuit pictures.