#include #include #include #include #include #include #include #include #include #include #include static const int MOD = 1000000007; using ll = long long; using u32 = uint32_t; using namespace std; template constexpr T INF = ::numeric_limits::max()/32*15+208; int main() { ll n; cin >> n; cout << n*3/2 << "\n"; return 0; }