#include<iostream>
#include<cstdio>
using namespace std;
#define ll long long
ll N;
int M;
int P=1;
ll pr[12];//素数
ll m[12];//余数
ll mo[12];
ll t[12];
ll ans;
void init()
{
	freopen("HanXin.in","r",stdin);
	freopen("HanXin.out","w",stdout);
	scanf("%lld%d",&N,&M);
	P=1;
	for(int i=1;i<=M;i++)
	{
		scanf("%lld%lld",&pr[i],&m[i]);
		P*=pr[i];
	}
}
void exGCD(ll a,ll b,ll &x,ll &y,ll &d)
{
    if(!b)
		x=1,y=0,d=a;
	else
		{exGCD(b,a%b,y,x,d),y-=(a/b)*x;}
}
ll work(ll a[],ll m[],ll n)
{ 
	ans=0;
	ll x,y,d,k;
    for(ll j=1;j<=n;j++)
	{
		k=P/m[j];
		exGCD(k,m[j],x,y,d);
        ans+=k*x*a[j];
		ans%=P;
    }
	if(ans<0)
		ans+=P;
	return ans;
}  
void out()
{
	ll temp=work(m,pr,M);
	if(temp>N)
		printf("%d\n",-1);
	else
		printf("%lld\n",(N-ans)%P);
	fclose(stdin);
	fclose(stdout);
}
int main()
{
	init();
	out();
	return 0;
}