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

double jiecheng(int num) {
    double result = 1.0;
    int i = 1;
    while (i <= num) {
        result *= i;
        i++;
    }
    return result;
}

int main() {
    double x, sinx = 0.0, term;
    int n;
    scanf("%lf %d", &x, &n);

    int i = 1;
    while (i <= n) {
        term = pow(-1, i - 1) * pow(x, 2 * i - 1) / jiecheng(2 * i - 1);
        sinx += term;
        i++;
    }

    printf("%.8lf", sinx);

    return 0;
}