#include <iostream>
#include <cassert>
#include <cmath>

using namespace std;

double lagrangeInterp(double x[], double y[], int n, double xL) {
    double sum = 0, mult;

    for (int i = 0; i < n; i++) {
        mult = 1;

        for (int j = 0; j < n; j++) {
            if (i != j) {
                assert(fabs(x[i] - x[j]) > 1e-10 && "Сannot be divided by zero!");

                mult *= (xL - x[j]) / (x[i] - x[j]);
            }
        }

        sum += mult * y[i];
    }

    return sum;
}

int main() {

    int n;

    cout << "Enter count of points: ";
    cin >> n;

    double x[n], y[n], xL;

    cout << "Enter x array: ";

    for (int i = 0; i < n; i++) {
        cin >> x[i];
    }

    cout << "Enter y array: ";

    for (int i = 0; i < n; i++) {
        cin >> y[i];
    }

    cout << "Enter x to find f(x): ";
    cin >> xL;

    cout << "f(" << xL << ") = " << lagrangeInterp(x, y, n, xL) << endl;

    return 0;
}