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

// dfmt off
T lread(T = long)(){return readln.chomp.to!T();}
T[] aryread(T = long)(){return readln.split.to!(T[])();}
void scan(TList...)(ref TList Args){auto line = readln.split();
foreach (i, T; TList){T val = line[i].to!(T);Args[i] = val;}}
alias sread = () => readln.chomp();enum MOD = 10 ^^ 9 + 7;
alias PQueue(T, alias less = "a<b") = BinaryHeap!(Array!T, less);
// dfmt on

void main()
{
    long H, N;
    scan(H, N);
    auto A = new long[](N);
    auto B = new long[](N);
    foreach (i; 0 .. N)
        scan(A[i], B[i]);
    auto dp = new long[](10 ^^ 4 * 2);
    foreach (i; 1 .. dp.length)
        dp[i] = long.max;
    long ans = long.max;
    foreach (i; 0 .. H)
        foreach (j; 0 .. N)
            if (dp[i] != long.max)
            {
                long damage = i + A[j];
                dp[damage] = min(dp[i] + B[j], dp[damage]);
                if (H <= damage)
                {
                    ans = min(ans, dp[damage]);
                }
            }
    writeln(ans);
}
