function main(input) {
  	input = input.split(" ");
  	var numberOfTrees = parseInt(input[0]);
    var D = parseInt(input[1]);
    var firstPoint = D + 1;
    var j = firstPoint + D;
    var checkModulo = numberOfTrees%j;
    if (checkModulo) {
        var i = numberOfTrees / j;
        return Math.trunc( i ) + 1;
    } else {
        return numberOfTrees / j;
    }
}
console.log(main(require('fs').readFileSync('/dev/stdin', 'utf8')));