#include<stdio.h>
long long gcd(long long x,long long y)
{
	if(y==0) return x;
	else return gcd(y,x%y);
}
long long exgcd(long long a,long long b,long long &d,long long &x,long long &y)
{
	if(!b)
	{
		d=a;
		x=1;
		y=0;
	}
	else
	{
		exgcd(b,a%b,d,y,x);
		y-=x*(a/b);
	}
}
long long abs(long long x)
{
	if(x>0) return x;
	else return -x;
}
long long a,b,d1,x1,y1;
int get(int a,int b)
{
	//scanf("%d%d",&a,&b);
	exgcd(a,-b,d1,x1,y1);
	x1=x1*(1/d1);
	int a1=a/d1;
	int b1=b/d1;
	b1=abs(b1);
	while(x1<=0)
	 {
	 	x1+=b1;
	 }
	while(x1>b1)
	 {
	 	x1-=b1;
	 }
	return x1;
	//printf("%d",x1);
	//while(1);
}
long long n,m;
long long p[101];
long long mod[101];
long long ans=1;
int main()
{
	freopen("HanXin.in","r",stdin);
	freopen("HanXin.out","w",stdout);
	scanf("%lld%lld",&n,&m);
	for(int i=1;i<=m;i++)
	{
		scanf("%lld%lld",&p[i],&mod[i]);
		ans*=p[i];
	}
	//printf("%lld\n",ans);
	long long x=0;
	long long ret=0;
	for(int i=1;i<=m;i++)
	{
		if(gcd(ans/p[i],p[i])!=1)
		{
			printf("-1");
			//printf("%lld %d\n",ans,100);
			//printf("%d",gcd(ans/p[i],p[i]));/;
			//while(1);
			return 0;
		}
		//printf("%lld\n",ans);
		x=get(ans/p[i],p[i])*ans/p[i];
		//printf("%d\n",x);
		ret+=x*mod[i];
	}
	//printf("%d\n",ret);
	long long l=0,r=n/ans;
	while(l<r)
	{
		//printf("%d ",l);
		//printf("%d\n",r);
		int mid=(l+r)/2;
		//printf("%d\n",ret+ans*mid);
		if(n>ret+ans*mid) l=mid+1;
		if(n<ret+ans*mid) r=mid;
 	}
 	printf("%lld",n-(ret+ans*(l-1)));
 	//while(1);
}