#include <iostream>
#include <iomanip>
#include <limits>

using namespace std;


int main() {
    double x, r = 0, p = 1;
    int n, i;


    do {
        if (cin.fail()) {
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
        }

        cout << "Enter x and n: ";
        cin >> x >> n;
    } while (cin.fail() || n <= 0);


    for (i = 1; i <= n; i++) {
        p *= (x / i);
        r += p;
    }
    r = r + 1;


    cout << "r = " << fixed << setprecision(4) << r << endl;
}