#include <iostream>
using namespace std;
int main()
{ int a,b,c;
cout << "a="; cin >> a;
cout << "b="; cin >> b;
cout << "c="; cin >> c;
if(b==((a+c)/2))
cout << "Numerele sunt in progresie aritmetica ";
else
cout << "Numerele nu sunt in progresie aritmetica ";
return 0;}