#include<cmath>

#include<cstdio>

#include<iostream>

#include<algorithm>

using namespace std;

int u[],d[];

int main()

{

    int n,m,ans,x;

    while(scanf("%d%d",&n,&m)!=EOF)

    {

        ans=2e9;

        for(int i=;i<=m;i++) scanf("%d%d",&u[i],&d[i]);

        for(int i=;i<=m;i++)

        {

            x=d[i]*n/(u[i]+d[i])+;

            ans=min(ans,u[i]*x-d[i]*(n-x));

        }

        printf("%d\n",ans);

    }

}