tiva c lunchpad (cortex m4)

hello i am trying to make a simple program .
i want to make edge interrupt with pin PF4 in the tive-c launchpad (cortex m4) and when i press that button the led blinks . thats all but i am facing problems i dont know whats wrong but the program is not working as expected

#include "C:\Keil\ARM\INC\TI\TM4C123\TM4C123GH6PM.h"

void delayMs(int n);
int main(void)
{
SYSCTL->RCGCGPIO |= 0x20; /* enable clock to PORTF */
/* PORTF0 has special function, need to unlock to modify */
GPIOF->LOCK = 0x4C4F434B; /* unlock commit register */
GPIOF->LOCK = 0; /* lock commit register */
/* configure PORTF for switch input and LED output */
GPIOF->DIR &= ~0x11; /* make PORTF4 input for switch */
GPIOF->DIR |= 0x0E; /* make PORTF3, 2, 1 output for LEDs */
GPIOF->DEN |= 0x1F; /* make PORTF4-0 digital pins */
GPIOF->PUR |= 0x11; /* enable pull up for PORTF4, 0 */
/* configure PORTF4, 0 for falling edge trigger interrupt */
GPIOF->IS &= ~0x11; /* make bit 4, 0 edge sensitive */
GPIOF->IBE &= ~0x11; /* trigger is controlled by IEV */
GPIOF->IEV &= ~0x11; /* falling edge trigger */
GPIOF->ICR |= 0x11; /* clear any prior interrupt */
GPIOF->IM |= 0x11; /* unmask interrupt */
/* enable interrupt in NVIC and set priority to 3 */
NVIC->IP[30] = 3 << 5; /* set interrupt priority to 3 */
NVIC->ISER[0] |= 0x40000000; /* enable IRQ30 (D30 of ISER[0]) */
__enable_irq(); /* global enable IRQs */
/* toggle the red LED (PF1) continuously */
while(1)
{
GPIOF->DATA |= 0x02;
delayMs(500);
GPIOF->DATA &= ~0x02;
delayMs(500);
}
}
/* SW1 is connected to PF4 pin, SW2 is connected to PF0. */
/* Both of them trigger PORTF interrupt */
void GPIOF_Handler(void)
{
int i;
volatile int readback;

/* toggle green LED (PF3) three times */
for (i = 0; i < 3; i++)
{
GPIOF->DATA |= 0x08;
//delayMs(500);
GPIOF->DATA &= ~0x08;
//delayMs(500);
}
GPIOF->ICR |= 0x11; /* clear the interrupt flag before return */
readback = GPIOF->ICR; /* a read to force clearing of interrupt flag */

}
/* delay n milliseconds (16 MHz CPU clock) */
void delayMs(int n)
{
int i, j;
for(i = 0 ; i < n; i++)
for(j = 0; j < 3180; j++)
{} /* do nothing for 1 ms */
}
/* This function is called by the startup assembly code to perform system specific
initialization tasks. */
void SystemInit(void)
{
__disable_irq(); /* disable all IRQs */
/* Grant coprocessor access */
/* This is required since TM4C123G has a floating point coprocessor */
SCB->CPACR |= 0x00F00000;
}

thanks in advance