This is returning -1. But it should be returning the number. I am not sure why its doing this can anyone help debug

public class BinarySearch{

public static void main(String args[]) {

int [] list = new int [] {1,3,6,10,15,19, 31, 34};

int target = 15;

System.out.println(binarySearch(list,target));

}

public static int binarySearch(int [] array, int target) {

int first = 0;

int last = array.length - 1;

int middle = 0;

while(last <= first) {

middle = last + (first - last)/2;

if(array[middle] == target) {

return array[middle];

}

if(target < array[middle]) {

last = middle - 1;

}

else {

first = middle + 1;

}

}

return -1;

}

}