C++ :

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int f[31000],v[30],w[30];
int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i=1;i<=m;i++)scanf("%d%d",&v[i],&w[i]);
    f[0]=0;
    for(int i=1;i<=m;i++)
    {
        for(int j=n;j>=v[i];j--)
        {
            f[j]=max(f[j],f[j-v[i]]+v[i]*w[i]);
        }
    }
    printf("%d\n",f[n]);
    return 0;
}

Pascal :

var n,m,w,c,i,j:longint;
   f:array[0..100000]of longint;
begin
  readln(n,m);
  for i:=1 to m do begin
    readln(w,c);
    c:=c*w;
    for j:= n downto w do
    if f[j-w]+c>f[j] then f[j]:=f[j-w]+c;
  end;
  for i:=2 to n do
  if f[i]>f[1] then f[1]:=f[i];
  writeln(f[1]);
end.