#include <fstream>
#include <string>
#include <algorithm>
using namespace std;
ifstream in("HanXin.in");
ofstream out("HanXin.out");
long long n,m,sum=1,cost=1,s=0;
class node
{
public:
	long long a;
	long long b;
}rest[11];
long long mark(long long x,long long y)
{
	//out<<x<<endl;
	if(x<n)
	{
		if(x<0)
		{
			out<<-1<<endl;
			return 0;
		}
		else
		{
		    out<<n-x<<endl;
		    return 0;
		}
	}
	mark(x-y,y);
}
long long compare(node x,node y)
{
	if(x.a<=y.a)return true;
	return false;
}
int main()
{
	long long i,j;
	in>>n>>m;
	for(i=1;i<=m;i++)in>>rest[i].a>>rest[i].b;
	sort(rest+1,rest+m+1,compare);
	for(i=1;i<=m;i++)sum*=rest[i].a;
	for(i=1;i<=m;i++)
	{
		cost=1;
		for(j=1;j<=m;j++)
		{
			cost*=rest[j].a;
		}
		cost/=rest[i].a;
		cost=rest[i].b*cost*(cost%rest[i].a);
		s+=cost;
	}
	if(s>n)
	{
		if(s>=sum)
		{
			out<<n-(s-(s-n+sum-1)/sum*sum)<<endl;
		}
		else out<<-1<<endl;
	}
	if(s==n)out<<0<<endl;
	if(s<n)out<<n-((n-s)/sum*sum)<<endl;
	//mark(175,180);
	in.close();
	out.close();
	return 0;
}