#include <iostream>
#include <cmath>
using namespace std;
int main() {
	//for6
	//float x;
	//cin >> x;
	//for (float i = 1.2; i < 2.1; i += 0.2) {
	//	cout << i * x << endl;
	//}
	//for26
	double x;
	int n;
	cin >> x >> n;
	double result = 0;
	long factorial = 1;
	double current_x = x;
	for (int i = 1; i <= 2 * n + 1; i += 2) {
		result += current_x / factorial;
		factorial *= (i + 1) * (i + 2);
		current_x *= -x * x;
	}
	cout << result;
	return 0;
}

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