#include<cstdio>

#include<algorithm>

#define N 210

using namespace std;

typedef long long ll;

typedef pair<ll,ll> PI;

ll m,f,l,r,len,m1,m2;PI s1,s2,ans;

int n,_n,i,j;struct P{ll p,s;}a[N];

bool cmp(const P&a,const P&b){return a.s==b.s?a.p<b.p:a.s>b.s;}

bool cmp2(const P&a,const P&b){return a.s<b.s;}

PI cal(ll k){

  ll t=m-f*k,d=0,now=0,j;

  for(i=1;i<=n;i++){

    if(a[i].s>=d)j=min(t/a[i].p/k,a[i].s-d+1),d+=j,now+=j*k,t-=j*a[i].p*k;

    if(a[i].s>=d)j=min(t/a[i].p,k),d++,now+=j,t-=j*a[i].p;

  }

  return PI(now,t);

}

int main(){

  while(~scanf("%lld%lld%d",&m,&f,&n)){

    for(i=1;i<=n;i++)scanf("%lld%lld",&a[i].p,&a[i].s);

    _n=n,sort(a+1,a+n+1,cmp);

    for(l=a[j=1].p,i=2;i<=n;i++){

      l=min(l,a[i].p);

      if(a[i].s<=a[j].s&&a[i].p>a[j].p)_n--,a[i].s=-1;else j=i;

    }

    sort(a+1,a+n+1,cmp),n=_n,sort(a+1,a+n+1,cmp2);

    l=1,r=m/(f+a[1].p);

    while(l<=r){

      len=(r-l)/3;

      if((s1=cal(m1=l+len))>(s2=cal(m2=r-len)))ans=max(ans,s1),r=m2-1;else ans=max(ans,s2),l=m1+1;

    }

    printf("%lld\n",ans.first);

    ans=PI(n=0,0);

  }

  return 0;

}