#include <stdio.h>
#include <math.h>

double calculate_sin(double x, int n) {
    double result = 0.0;
    double term = x;
    double sign = 1.0;
    
    int i;
    for (i = 1; i <= n; ++i) {
        result += sign * term;
        sign = -sign;
        term *= x * x / ((2 * i) * (2 * i + 1));
    }

    return result;
}

int main() {
    double x;
    int n;

    scanf("%lf %d", &x, &n);


    double sin_x = calculate_sin(x, n);

    printf("%.8lf\n", sin_x);

    return 0;
}