#include<iostream>
#include<cstdio>
#include<cstring>
#include <algorithm>
#include <math.h>
using namespace std;
typedef long long LL;
int main()
{
    int n,m;
    while(scanf("%d%d",&n,&m)!=EOF){
        int MIN = 999999999;
        for(int i=1;i<=m;i++){
            int a,b;
            scanf("%d%d",&a,&b);
            int k = n/a+((n%a==0)?0:1);
            MIN = min(MIN,b*k);
        }
        printf("%d\n",MIN);
    }
    return 0;
}