#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>#include <stdlib.h>#include <stdio.h>
#include <pthread.h>
#include <linux/sem.h>
#include <linux/shm.h>int main( int   argc,          char *argv[] ){	pid_t p1,p2,p3,p4;
	pid_t	t1,t2,t3,t4;
	int status;		if((p1=fork())==0)	{			execv("./first",NULL);			}else {				if((p2=fork())==0)	{					execv("./second",NULL);					}else{						if((p3=fork())==0)	{						execv("./third",NULL);						}else{						waitpid(p1,&status,0);
						waitpid(p2,&status,0);						waitpid(p3,&status,0);						}					}			}        return 0;}