/* AUTHOR: TUAN ANH - BUI */
// ~~ icebear ~~
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> ii;
typedef pair<int, ii> iii;
template<class X, class Y>
bool minimize(X &x, const Y &y) {
if (x > y) return x = y, true;
return false;
}
template<class X, class Y>
bool maximize(X &x, const Y &y) {
if (x < y) return x = y, true;
return false;
}
#define FOR(i,a,b) for(int i=(a); i<=(b); ++i)
#define FORR(i,a,b) for(int i=(a); i>=(b); --i)
#define REP(i, n) for(int i=0; i<(n); ++i)
#define RED(i, n) for(int i=(n)-1; i>=0; --i)
#define MASK(i) (1LL << (i))
#define BIT(S, i) (((S) >> (i)) & 1)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define all(x) x.begin(), x.end()
#define task "icebear"
/*END OF TEMPLATE. ICEBEAR AND THE CAT WILL WIN VOI26 */
const int MOD = 1e9 + 7;
const int inf = (int)1e9 + 27092008;
const ll INF = (ll)1e18 + 27092008;
const int N = 2000 + 5;
int numPiece, numChoose;
ii piece[N];
ll f[N][N];
void init(void) {
cin >> numPiece >> numChoose;
FOR(i, 1, numPiece) cin >> piece[i].fi >> piece[i].se;
}
void process(void) {
sort(piece + 1, piece + numPiece + 1, [&](const ii &x, const ii &y){return x.se < y.se;});
FOR(i, 0, numPiece) FOR(j, 0, numChoose) f[i][j] = -INF;
FOR(i, 1, numPiece) FOR(j, 1, numChoose) {
f[i][j] = f[i - 1][j];
if (j == 1) maximize(f[i][j], piece[i].fi + 2 * piece[i].se);
else if (j < numChoose) maximize(f[i][j], f[i - 1][j - 1] + piece[i].fi);
else maximize(f[i][j], f[i - 1][j - 1] + piece[i].fi - 2 * piece[i].se);
}
cout << f[numPiece][numChoose];
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
if (fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
int tc = 1;
// cin >> tc;
while(tc--) {
init();
process();
}
return 0;
}
