STM32F407VG DISCOVERY BOARD DELAY FUNCTION PROBLEMf

Hi, I have a problem. I want to create a 1 second delay. My IDE is KEIL, my board is STM32F407. My HSE_VALUE is 8000000 and my PLL_M is 8. But my led is constantly on. 

#include "stm32f4xx.h" // Device header

void delay(uint32_t );

void delay(uint32_t time)
{
while(time--);
}

int main()
{
GPIO_InitTypeDef GPIO_InitStructure;

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD,ENABLE);

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
GPIO_Init(GPIOD, &GPIO_InitStructure);


while(1)
{
GPIO_SetBits(GPIOD, GPIO_Pin_13);
delay(21000000);
GPIO_ResetBits(GPIOD, GPIO_Pin_13);
delay(21000000);
}

}