#include<bits/stdc++.h> using namespace std; const int maxm=2001,maxn=31; int n,m,v,i; int c[maxn],w[maxn]; int f[maxm]; int main() { scanf("%d%d",&m,&n); for(i=1;i<=n;i++) scanf("%d%d",&w[i],&c[i]); for(i=1;i<=n;i++) for(v=w[i];v<=m;v++) if(f[v-w[i]]+c[i]>f[v]) f[v]=f[v-w[i]]+c[i]; cout<<f[m]/2<<endl; return 0; }