#include <bits/stdc++.h>
using namespace std;
const int MAXN = 60;
int p[MAXN], l[MAXN], r[MAXN];
pair<int, int> memo[MAXN][MAXN];
#define OPEN 0
int c;
const int INF = 1e9 + 10;
int calc(int pl, int pr, int la, int ra) {
return (p[pr] - p[pl])*(l[la + 1] + r[ra + 1]);
}
pair<int, int> dfs(int ll, int rr) {
if (memo[ll][rr].first != -1) {
assert(memo[ll][rr].second != -1);
return memo[ll][rr];
}
int fir, sec;
if(rr!=c)
sec = min(dfs(ll, rr - 1).second + calc(rr - 1, rr, ll - 1, rr), dfs(ll, rr - 1).first + calc(ll, rr, ll - 1, rr));
else sec=INF;
if(ll!=c)
fir = min(dfs(ll + 1, rr).first + calc(ll, ll + 1, ll, rr + 1), dfs(ll + 1, rr).second + calc(ll, rr, ll, rr + 1));
else fir=INF;
memo[ll][rr].first = fir;
memo[ll][rr].second = sec;
return memo[ll][rr];
}
int main() {
#if OPEN
freopen("in.txt", "r", stdin);
#endif
int n;cin >> n >> c;
int power[MAXN];
int minpos = INF;
int maxpos = -INF;
c -= 1;
for (int i = 0;i<n;i++) {
cin >> p[i] >> power[i];
minpos = min(minpos, p[i]);
maxpos = max(maxpos, p[i]);
}
if (n == 1) {
cout << 0 << endl;
return 0;
}
memset(l, 0, sizeof(l));
memset(r, 0, sizeof(r));
for (int i = 0;i<MAXN;i++)
for (int j = 0;j<MAXN;j++)
memo[i][j].first = memo[i][j].second = -1;
int sum = 0;
for (int i = 0;i<n;i++) {
sum += power[i];
l[i + 1] = sum;
}
sum = 0;
for (int i = 0;i<n;i++) {
sum += power[n - 1 - i];
r[n + 1 - 1 - i] = sum;
}
if (p[c]>minpos) {
memo[c - 1][c].first = (p[c] - p[c - 1])*(l[c + 1 - 1] + r[c + 1 + 1]);
memo[c - 1][c].second = INF;
}
if (p[c]<maxpos) {
memo[c][c + 1].second = (p[c + 1] - p[c])*(r[c + 1 + 1] + l[c + 1 - 1]);
memo[c][c + 1].first = INF;
}
int ans = min(dfs(0, n - 1).first, dfs(0, n - 1).second);
cout << ans << endl;
return 0;
}