function main(input) {
//Enter your code here
var data = input.split('
');
var firstLine = data[0].split(' ');
var len = firstLine[0];
//process.stdout.write('length:'+len);
var toFind = firstLine[1];
//process.stdout.write('toFind:'+toFind);
//process.stdout.write('
');
var arr = data[1].split(' ');
//process.stdout.write(arr);
for(var i=len-1;i>=0;i--) {
if(arr[i] == toFind){
process.stdout.write(i+1);
return;
}
}
process.stdout.write(-1);
}