import core.bitop, std.algorithm, std.ascii, std.bigint, std.conv,
    std.functional, std.math, std.numeric, std.range, std.stdio, std.string,
    std.random, std.typecons, std.container;

ulong MAX = 1_000_100, MOD = 1_000_000_007, INF = 1_000_000_000_000;
alias sread = () => readln.chomp();
alias lread(T = long) = () => readln.chomp.to!(T);
alias aryread(T = long) = () => readln.split.to!(T[]);
alias Pair = Tuple!(long, "damage", long, "cost");
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);

void main()
{
    long h, n;
    scan(h, n);
    auto magic = new Pair[](n);
    foreach (ref e; magic)
    {
        long a, b;
        scan(a, b);
        e = Pair(a, b);
    }
    auto d = new long[](MAX);
    d[] = INF;
    d[0] = 0;
    foreach (i; iota(h + 1))
    {
        foreach(j; iota(n))
        {
            d[i + magic[j].damage] = min(d[i] + magic[j].cost, d[i + magic[j].damage]);
        }
    }
    long ans = INF;
    foreach (i; iota(h, MAX))
    {
        ans = min(d[i], ans);
    }
    ans.writeln();
}

void scan(TList...)(ref TList Args)
{
    auto line = readln.split();
    foreach (i, T; TList)
    {
        T val = line[i].to!(T);
        Args[i] = val;
    }
}
