Codeforces Round #137 (Div. 2) A

Codeforces Round #137 (Div. 2) A.cpp

//by Brickgao
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>

using namespace std;

__int64 a[100100];

int main()
{
    __int64 n, k, ans, i;
    bool flag;
    while(~scanf("%I64d%I64d", &n, &k))
    {
        for(i = 1; i <= n; i++)
            scanf("%I64d", &a[i]);
        flag = true;
        for(i = k + 1; i <= n; i++)
            if(a[k] != a[i])
            {
                flag = false;
                break;
            }
        if(!flag)
        {
            printf("-1\n");
        }
        else
        {
            for(i = k - 1; i >= 1; i --)
                if(a[i] != a[k])
                    break;
            ans = i;
            printf("%I64d\n", ans);
        }
    }
    return 0;
}