C++ :

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int n,a,b;
struct _{int a,b;}__[10003];
bool pp(_ a,_ b){return a.b*a.a<b.b*b.a;};
struct big{
	int n;
	int a[16003];
	void operator*=(int b){
		for(int i=0;i<n;++i)
		a[i]*=b;
		for(int i=0;i<n;++i)
		if(a[i]>9){
			a[i+1]+=a[i]/10;
			a[i]%=10;
		}
		while(a[n]>9){
			a[n+1]=a[n]/10;
			a[n]%=10;
			++n;
		}
		if(a[n])++n;
	}
	bool operator>(big b){
		if(n!=b.n)
		return n>b.n?1:0;
		for(int i=n-1;i>=0;++i)
		if(a[i]!=b.a[i])
		return a[i]>b.a[i]?1:0;
		return 0;
	}
	big operator/(int b){
		bool flag=0;
		big res;
		memset(res.a,0,sizeof res.a);
		res.n=0;
		int now=0;
		for(int i=n-1;i>=0;--i){
			now=now*10+a[i];
			if(now>=b){
				if(!flag)
				res.n=i+1,flag=1;
				res.a[i]=now/b;
				now%=b;
			}
		}
		return res;
	}
}now,ans;
int main(){
	scanf("%d%d%d",&n,&a,&b);
	for(int i=0;i<n;++i)
	scanf("%d%d",&__[i].a,&__[i].b);
	sort(__,__+n,pp);
	while(a){
		now.a[now.n++]=a%10;
		a/=10;
	}
	for(int i=0;i<n;++i){
		big stay=now/__[i].b;
		ans=ans>stay?ans:stay;
		now*=__[i].a;
	}
	for(int i=ans.n-1;i>=0;--i)
	printf("%d",ans.a[i]);
	return 0;
}

Pascal :

var n,i,j,t:longint;d,ans,max,e:ansistring;
    a,b,c:array[1..1010]of longint;
function gcd2(a:ansistring;b:longint):ansistring;
var i,j,lena,lenc,c:longint;
    x,y:array[1..4010]of longint;
begin
  fillchar(x,sizeof(x),0);
  fillchar(y,sizeof(y),0);
  lena:=length(a);
  for i:=1 to lena do
    x[i]:=ord(a[i])-48;
  c:=0;
  for i:=1 to lena do
    begin
      y[i]:=(c*10+x[i]) div b;
      c:=(c*10+x[i]) mod b;
    end;
  lenc:=1;
  while (y[lenc]=0)and(lenc<lena) do inc(lenc);
  gcd2:='';
  for i:=lenc to lena do gcd2:=gcd2+chr(y[i]+48);
end;
function gcd1(a,b:ansistring):ansistring;
var i,j,lena,lenb,lenc:longint;
    x,y,z:array[1..4010]of longint;
begin
  fillchar(x,sizeof(x),0);
  fillchar(y,sizeof(y),0);
  fillchar(z,sizeof(z),0);
  lena:=length(a);
  lenb:=length(b);
  for i:=1 to lena do
    x[i]:=ord(a[lena+1-i])-48;
  for i:=1 to lenb do
    y[i]:=ord(b[lenb+1-i])-48;
  for i:=1 to lena do
    for j:=1 to lenb do
      begin
        z[i+j-1]:=z[i+j-1]+x[i]*y[j];
        z[i+j]:=z[i+j]+z[i+j-1] div 10;
        z[i+j-1]:=z[i+j-1] mod 10;
      end;
  lenc:=lena+lenb;
  while (lenc>1)and(z[lenc]=0) do dec(lenc);
  gcd1:='';
  for i:=lenc downto 1 do gcd1:=gcd1+chr(z[i]+48);
end;
begin
  read(n);
  for i:=1 to n+1 do
    begin
      read(a[i],b[i]);
      c[i]:=a[i]*b[i];
    end;
  for i:=2 to n do
    for j:=i+1 to n+1 do
      if c[i]>c[j] then
        begin
          t:=a[i];a[i]:=a[j];a[j]:=t;
          t:=b[i];b[i]:=b[j];b[j]:=t;
          t:=c[i];c[i]:=c[j];c[j]:=t;
        end;
  str(a[1],ans);
  max:='0';e:='0';
  for i:=2 to n+1 do
    begin
      str(a[i],d);
      e:=gcd2(ans,b[i]);
      ans:=gcd1(ans,d);
      if (length(e)>length(max))or((length(e)=length(max))and(e>max)) then
        max:=e;
    end;
  writeln(max);
end.