Blink program with STM32L475 VG Discovery

Hi, I'm a french student and I'm trying to use a STM32L475 VG Discovery kit with Arduino IDE for a project. I downloaded the last version of the softwar and then, I installed the libraries for STM32. The first program I tried to run was this one:

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);                       // wait for a second
  digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);                       // wait for a second
}

The problem is that during the compilation ther is an error message:

c:\users\mathi\appdata\local\arduino15\packages\stm32\tools\arm-none-eabi-gcc\6-2017-q2-update\bin../lib/gcc/arm-none-eabi/6.3.1/../../../../arm-none-eabi/bin/ar.exe: unable to rename 'core\core.a'; reason: File exists

exit status 1
Erreur de compilation pour la carte Discovery

Can you help me and tell me what to do please? Thannks