Tests for this probel are very weak.
Here it is code, that gets AC sn 0.488
you must have weak tests or very good computers=)
[code]
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>

using namespace std;
#define pb push_back

int i,j,a,b,n,m,k;
vector <int> mas;

int main()
{
    scanf("%d",&m);
    scanf("%d",&a);
    n=0;
    mas.clear();
    while (a!=-1)
    {
          mas.pb(a);
          scanf("%d",&a);
          n++;
    }
    for (i=0;i<n-m+1;i++)
    {
        printf("%d\n",*max_element(mas.begin()+i,mas.begin()+i+m));
    }
}
[/code]
So in my opinion you should add a test like this:
14000
1
2
3
...
25000
-1

or if even this program can pass it - decrease timelimit..thanks