Ultrasonics sensors HC-SR04

Hello,
I have a problem with my two ultrasonics sensors. there are fonctional when I connect one by one but they don't work together, in same time.

My test code :

/* Sensor ultrasonic HC-SR04 */

long lecture_echo1; // 1er sensor
long cm1;
long lecture_echo2; // 2nd sensor
long cm2;

void setup() 
{ 
  Serial.begin(9600); 
  pinMode(9, INPUT); // 9 = trig US back
  digitalWrite(9, LOW);
  pinMode(8, INPUT); // 8 =  echo US back
  
  pinMode(12, OUTPUT); // 12 = trig US front
  digitalWrite(12, LOW);
  pinMode(11, INPUT); // 11 = echo US front
}

void loop() 
{ 
  digitalWrite(9, HIGH); 
  delayMicroseconds(10); 
  digitalWrite(9, LOW); 
  lecture_echo1 = pulseIn(8, HIGH); 
  cm1 = lecture_echo1 / 58;
  Serial.print("Distance en cm1 : "); // display
  Serial.println(cm1);
  delay(500);
  
  digitalWrite(12, HIGH); 
  delayMicroseconds(10); 
  digitalWrite(12, LOW); 
  lecture_echo2 = pulseIn(11, HIGH); 
  cm2 = lecture_echo2 / 58;
  Serial.print("Distance en cm2 : "); 
  Serial.println(cm2); // display 
  delay(500); 
}

thanks for your help,

You have defined pin 9 to be input, but are using it as an output.