#include <algorithm> #include <iostream> #include <iomanip> #include <cstring> #include <string> #include <vector> #include <random> #include <bitset> #include <queue> #include <cmath> #include <stack> #include <set> #include <map> typedef long long ll; using namespace std; int main() { cin.sync_with_stdio(false); cin.tie(0); ll n, m; cin >> n >> m; ll a[n], b[n]; for (int i = 0; i < n; i++) cin >> a[i] >> b[i]; vector <ll> opt(n+1, 0); vector <ll> mx(n+1, 0); for (int i = 0; i < n; i++) { opt[i+1] = max(a[i], b[i]) + opt[i]; mx[i+1] = max(mx[i], opt[i+1]); } vector <ll> sm(n+1, 0); for (int i = 0; i < n; i++) { ll val = max({b[i], (m-1)*a[i] + b[i], m*a[i]}); sm[i+1] = sm[i] + val; } ll ans = - (1LL << 60); for (int k = 1; k <= n; k++) { ans = max(ans, sm[k] + (mx[n] - mx[k])); } cout << ans << "\n"; return 0; }