#include <stdio.h>

int main(void) {
    double x;
    int n;
    scanf("%lf %d", &x, &n);

    int fact = 1;
    double ans = 0, deg = x;
    for (int i = 1; i <= n * 2 - 1; i += 2) {
        double c = deg / fact;
        if ((i / 2) % 2 == 0) {
            ans += c;
        } else {
            ans -= c;
        }
        fact *= (i + 1);
        fact *= (i + 2);
        deg *= x * x;
    }

    printf("%.6f", ans);
    return 0;
}