#include <iostream>
#include <cmath>

using namespace std;

double lagrangeInterp(double x[], double y[], int n, double x0) {
	double sum = 0, mult;

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

		for (int j = 0; j < n; j++)
			if (i != j) 
				mult *= (x0 - x[j]) / (x[i] - x[j]);
		sum += mult * y[i];
	}

	return sum;
}

int main() {

	const int n = 5;
	double x0;

	double x[n]  {0, 1, 2, 3, 4};
	double y[n]  {1, -1, 0, 10, 35};

	cout << "Enter x: ";
	cin >> x0;

	cout << "f(" << x0 << ") = " << lagrangeInterp(x, y, n, x0) << endl;

	return 0;
}