Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.

For example,
Given 1->1->2, return 1->2.
Given 1->1->2->3->3, return 1->2->3.

#include<stdio.h>  
#include<stdlib.h>  
  
typedef struct ListNode {  
    int val;  
    struct ListNode *next;  
}ListNode;  

ListNode *deleteDuplicates(ListNode *head) {
    ListNode *p1=head,*p2=head;
    if(head==NULL) return head;
    while(p1->next!=NULL && p2!=NULL){
        if(p1->next->val==p1->val) {
            p2->next=p2->next->next;
            p1=p2;
        }
        else {
            p2=p1;
            p1=p1->next;
        }
    }        
    return head;
}

void main(){
    ListNode *p1,*p2,*head;
    int i;
    p1=(ListNode*)malloc(sizeof(ListNode));
    scanf("%d",&p1->val);
    for(i=1;p1->val!=0;i++){
        if(i==1) head=p1;
        else p2->next=p1;
        p2=p1;
        p1=(ListNode*)malloc(sizeof(ListNode));
        scanf("%d",&p1->val);
    }
    p2->next=NULL;
    head=deleteDuplicates(head);
    for(p1=head;p1!=NULL;p1=p1->next) printf("%d\n",p1->val);
}