#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<vector>
#include<queue>
using namespace std;

#define X first
#define Y second

typedef pair<int,int> pii;
typedef long long LL;
const char nl = '\n';
const int N = 1e5+10;
const int M = 1e6+10;
int n,m;
int b[N],x[N];
LL dp[N];

void solve(){
    cin >> n >> m;
    memset(dp,0x3f,sizeof dp);
    dp[n] = 0;
    for(int i = 1; i <= m; i ++)cin >> b[i] >> x[i];
    for(int i = n; i >= 1; i --){
        for(int j = 1; j <= m; j ++){
            if(i%x[j] && i >= i % x[j])dp[i-i%x[j]] = min(dp[i-i%x[j]],dp[i] + b[j]);
        }
    }
    for(int i = 1; i <= n; i ++){
        if(dp[i] != dp[1]){
            cout << dp[i];
            return;
        }
    }
    cout << 0;	//别漏了特殊情况
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0),cout.tie(0);

    solve();
}