#include <iostream>
using namespace std;

int main() {

    bool isIncorrect;
    int precision;

    do {
        isIncorrect = false;

        cout << "Enter precision (number of iterations) : ";
        cin >> precision;

        if (cin.fail()) {
            cin.clear();
            cin.ignore();
            isIncorrect = true;
        }

        if (!isIncorrect && (precision <= 0)) {
            isIncorrect = true;
        }

        if (isIncorrect) {
            cout << "Input Error. Check if the data is correct." << endl;
        }

        while (cin.get() != '\n');
    } while (isIncorrect);

    double pi = 0.0;
    float numerator = 1;
    float firstDenominator = 1;
    float secondDenominator = 3;

    for (int i = 0; i < precision; i++) {
        for(int k = 0; k < 3; k++){
            if (k < 2){
                pi += numerator/(firstDenominator*secondDenominator);
            } else {
                pi -= numerator/(firstDenominator*secondDenominator);
            }
            firstDenominator+=4;
            secondDenominator+=4;
        }
    }

    cout << "Pi value = " << pi*8;

    return 0;

}