#include <bits/stdc++.h>
using namespace std;
const int N = 100;
int f[N][N], g[N][N], a[N], sum[N], b[N];
int main()
{
memset(f, 0x3f, sizeof f);
int n, c;
cin >> n >> c;
for (int i = 1; i <= n; i ++ )
{
cin >> a[i] >> b[i];
sum[i] = b[i] + sum[i - 1];
}
f[c][c] = g[c][c] = 0;
for (int l = 2; l <= n; l ++ )
for (int i = 1; i + l - 1 <= n; i ++ )
{
int j = i + l - 1;
f[i][j] = min(f[i + 1][j] + (a[i + 1] - a[i]) * (sum[i] + sum[n] - sum[j]),
g[i + 1][j] + (a[j] - a[i]) * (sum[i] + sum[n] - sum[j]));
g[i][j] = min(f[i][j - 1] + (a[j] - a[i]) * (sum[i - 1] + sum[n] - sum[j - 1]),
g[i][j - 1] + (a[j] - a[j - 1]) * (sum[i - 1] + sum[n] - sum[j - 1]));
}
int ans = min(f[1][n], g[1][n]);
cout << ans << endl;
return 0;
}