var f:array[0..1000,0..1000]of longint;

sum,a,b:array[1..1000]of longint;

ans,i,j,n,m,k,o,p,t:longint;

function max(a,b:ilongint):longint;

begin

if a>b then exit(a) else exit(b);

end;

begin

readln(n,m);

for i:=1 to n do

begin

readln(a[i],b[i]);

if i=1 then sum[i]:=a[i] else sum[i]:=a[i]+sum[i-1];

end;

for i:=1 to n do f[i,0]:=sum[i]*b[1];

for i:=2 to n do

begin

if i-1<m then t:=i-1 else t:=m;

for j:=1 to t do

for k:=j to i-1 do

f[i,j]:=max(f[k,j-1]+(sum[i]-sum[k])*b[k+1],f[i,j]);end;

ans:=0;

for i:=1 to n do if ans<f[i,m]) then ans:=f[i,m];

writeln(ans);

end.