int binsearch(int x, int v[], int n)
{
int m = n / 2, r;
if(n < 1) return -1;
if(v[m] > x) return binsearch(x, v, m);
if(v[m] == x) return m;
r = binsearch(x, v + m + 1, n - m - 1);
if(r >= 0) r += m + 1;
return r;
}