#include <iostream>
#include <math.h>

using namespace std;

int main() {
  int n;
  cout << "Amount of operations:";
  cin >> n;

  int xi;
  float EX, p, result = 0;

  cout << "Provide EX:";
  cin >> EX;

  for(int i = 0; i < n; i += 1) {
    cout << "\nStep " << i + 1 << endl;
    cout << "Provide current x:";
    cin >> xi;
    cout << "Provide current p:";
    cin >> p;

    result += pow((xi - EX), 2) * p;
  }

  cout << "\nVar(X) = " << result;
  cout << "\nD(X) = " << sqrt(result);
}