#include <bits/stdc++.h>
using namespace std;
#define int long long
#define isz(a) (int)(a).size()
const int NM = 300, inf = 1e18;
int N, K, H[NM+5], C[NM+5], tmpH[NM+5], tmpC[NM+5];
vector <int> od;
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> N >> K;
for (int i = 1; i <= N; i++)
cin >> H[i] >> C[i];
if (N == 1){
cout << "0\n";
return 0;
}
int ans = +inf;
for (int i = 1; i <= N; i++){
int res = 0;
for (int j = 1; j <= N; j++){
tmpC[j] = 0;
if (j == i){
tmpH[j] = H[j];
continue;
}
tmpH[j] = max(H[i]+1, H[j]);
res += (tmpH[j]-H[j])*K;
}
od.clear();
for (int j = 1; j <= N; j++) od.push_back(j);
sort(od.begin(), od.end(), [&](int x, int y){
return tmpH[x] < tmpH[y];
});
for (int j = 1; j < isz(od); j++){
int kbest = -1;
for (int k = 0; k < j; k++){
if (tmpH[od[k]] == tmpH[od[j]]) break;
if (kbest == -1 || tmpC[od[k]] < tmpC[od[kbest]]){
kbest = k;
}
}
res += tmpC[od[kbest]];
if (tmpC[od[kbest]] == 0){
tmpC[od[kbest]] = C[od[kbest]];
}
}
ans = min(ans, res);
}
cout << ans;
return 0;
}
