#include <bits/stdc++.h>
using namespace std;
#define all(x) x.begin(), x.end()
#define pb push_back
#define ln '\n'
#define int long long
template <class _T>
bool chmin(_T &x, const _T &y){
bool flag = false;
if ( x > y ){
x = y; flag |= true;
}
return flag;
}
template <class _T>
bool chmax(_T &x, const _T &y){
bool flag = false;
if ( x < y ){
x = y; flag |= true;
}
return flag;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int n, m; cin >> n >> m;
vector <pair<int,int>> g[n + m];
vector <int> p;
for ( int i = 1; i < n + m; i++ ){
int x, w; cin >> x >> w;
g[--x].pb({i, w});
p.pb(w);
}
assert(n == 1);
sort(all(p));
int res = 0;
for ( auto i: p ){
res += abs(i - p[m >> 1]);
}
cout << res;
cout << '\n';
}
