CodeForces 447-A. DZY Loves Hash

A. DZY Loves Hash

time limit per test

1 second

memory limit per test

256 megabytes

input

standard input

output

standard output

DZY has a hash table with p buckets, numbered from 0 to p - 1. He wants to insert n numbers, in the order they are given, into the hash table. For the i-th number xi, DZY will put it into the bucket numbered h(xi), where h(x) is the hash function. In this problem we will assume, that h(x) = x mod p. Operation a mod b denotes taking a remainder after division a by b.

However, each bucket can contain no more than one element. If DZY wants to insert an number into a bucket which is already filled, we say a "conflict" happens. Suppose the first conflict happens right after the i-th insertion, you should output i. If no conflict happens, just output -1.

Input

The first line contains two integers, p and n (2 ≤ p, n ≤ 300). Then n lines follow. The i-th of them contains an integer xi (0 ≤ xi ≤ 109).

Output

Output a single integer — the answer to the problem.

Sample test(s)

input

10 5
0
21
53
41
53

output

4

input

5 5
0
1
2
3
4

output

-1

#include<stdio.h>
#include<iostream>
#include<string.h>
using namespace std;
int main()
{
    int a[310],num[310];
    memset(num,0,sizeof(num));
    int p,n;
    scanf("%d%d",&p,&n);
    for(int i = 0; i < n;i++)
    {
        scanf("%d",&a[i]);
    }
    int flag = 0;
    int ans = 0;
    for(int i = 0;i < n;i++)
    {
        if(num[a[i]%p] == 0)
            num[a[i]%p]++;
        else
        {
            flag = 1;
            ans = i+1;
            break;
        }
    }
    if(flag) printf("%d\n",ans);
    else printf("-1\n");
    return 0;
}