if let line1 = readLine(),
   let CN = line1.split(separator: " ").compactMap({Int($0)}) as? [Int],
   let C = CN.first, let N = CN.last
{
    var info: [(cost: Int, customer: Int)] = []
    for _ in 1...N {
        guard let line2 = readLine(),
              let cost_customer = line2.split(separator: " ").compactMap({Int($0)}) as? [Int],
              let cost = cost_customer.first, let customer = cost_customer.last
        else { break }
            
        info.append((cost: cost, customer: customer))
    }
    
    var dp: [Int] = Array(repeating: Int.max, count: C + 101)
    dp[0] = 0
    
    for (cost, customer) in info {
        for i in customer...(C+100) {
            if dp[i-customer] != Int.max {
                dp[i] = min(dp[i], dp[i-customer] + cost)
            }
        }
    }
    
    print(dp[C...].min()!)
}