// Slower C++ solution:
#include<bits/stdc++.h>

using namespace std;

#define fi first

#define se second

#define pb push_back

#define rep(i,n) for(int i = 0; i < (n); ++i)

#define rrep(i,n) for(int i = 1; i <= (n); ++i)

#define drep(i,n) for(int i = (n)-1; i >= 0; --i)

#define srep(i,s,t) for (int i = s; i < t; ++i)

#define rng(a) a.begin(),a.end()

#define rrng(a) a.rbegin(),a.rend()

#define uni(x) x.erase(unique(rng(x)),x.end())

#define PQ(T) priority_queue<T,v(T),greater<T> >

#define dup(x,y) (((x)+(y)-1)/(y))

#define v(T) vector<T>

#define vv(T) v(v(T))

#define diup(v,a,k) distance((v).begin(),(k)+upper_bound((v).begin(),(v).end(),(a)))

#define dilo(v,a,k) distance((v).begin(),(k)+lower_bound((v).begin(),(v).end(),(a)))

using ll = int64_t;

using ull = uint64_t;

using uint = uint32_t;

using pii = pair<int,int>;

using pll = pair<ll,ll>;

using pil = pair<int,ll>;

using vi = vector<int>;

using vvi = vector<vi>;

using vl = vector<ll>;

template<typename T>inline istream& operator>>(istream&i,v(T)&v)

{rep(j,v.size())i>>v[j];return i;}

template<typename T>string join(const v(T)&v)

{stringstream s;rep(i,v.size())s<<' '<<v[i];return s.str().substr(1);}

template<typename T>inline ostream& operator<<(ostream&o,const v(T)&v)

{if(v.size())o<<join(v);return o;}

template<typename T1,typename T2>inline istream& operator>>(istream&i,pair<T1,T2>&v)

{return i>>v.fi>>v.se;}

template<typename T1,typename T2>inline ostream& operator<<(ostream&o,const pair<T1,T2>&v)

{return o<<v.fi<<","<<v.se;}

const double eps = 1e-6;

const ll LINF = 100200300400500600ll;

const int INF = 1001001001;

//--------------------------------------------------------

#define fastio cin.tie(nullptr); std::ios::sync_with_stdio(false);

#define myio ifstream iofi; if(argc>1){iofi.open(argv[1]); std::cin.rdbuf(iofi.rdbuf());}

#define myloopset int loop = 1; if(argc>2) loop =stoi(argv[2]); rep(i,loop)

//--------------------------------------------------------------

template <class T> T chmin(T &a,T b){if(a>b){a=b; return 1;}else return 0;}

template <class T> T chmax(T &a,T b){if(a<b){a=b; return 1;}else return 0;}

const int dx[4] = {0,1,0,-1};

const int dy[4] = {-1,0,1,0};



struct D21{

  int is,js;

  D21(int isize,int jsize){

    is = isize;

    js = jsize;

  }

  int operator()(int i,int j){

    return i*js+j;

  }

};





void Main(){

  int h,n;

  cin>>h>>n;

  vi a(n),b(n);

  rep(i,n){

    cin>>a[i]>>b[i];

  }

  int p = 10000;

  vvi dp(n+1,vi(h+p,INF));

  rep(i,n+1) dp[i][0] = 0;

  rep(i,n) rep(j,h+p){

    dp[i+1][j] = min( dp[i+1][j] ,dp[i][j]);

    if( j >= a[i] )

      dp[i+1][j] = min( dp[i+1][j] ,dp[i+1][j - a[i]] + b[i] );

  }

  int ans = dp[n][h];

  srep(i,h+1,h+p){

    chmin(ans,dp[n][i]);

  }

  cout<<ans<<endl;

} int main(int argc,char** argv)

{fastio; myio; myloopset Main();}


// Faster C++ solution for the same problem (measured speedup: 1.6017777844692893x):
#include<bits/stdc++.h>

using namespace std;

#define fi first

#define se second

#define pb push_back

#define rep(i,n) for(int i = 0; i < (n); ++i)

#define rrep(i,n) for(int i = 1; i <= (n); ++i)

#define drep(i,n) for(int i = (n)-1; i >= 0; --i)

#define srep(i,s,t) for (int i = s; i < t; ++i)

#define rng(a) a.begin(),a.end()

#define rrng(a) a.rbegin(),a.rend()

#define uni(x) x.erase(unique(rng(x)),x.end())

#define PQ(T) priority_queue<T,v(T),greater<T> >

#define dup(x,y) (((x)+(y)-1)/(y))

#define v(T) vector<T>

#define vv(T) v(v(T))

#define diup(v,a,k) distance((v).begin(),(k)+upper_bound((v).begin(),(v).end(),(a)))

#define dilo(v,a,k) distance((v).begin(),(k)+lower_bound((v).begin(),(v).end(),(a)))

using ll = int64_t;

using ull = uint64_t;

using uint = uint32_t;

using pii = pair<int,int>;

using pll = pair<ll,ll>;

using pil = pair<int,ll>;

using vi = vector<int>;

using vvi = vector<vi>;

using vl = vector<ll>;

template<typename T>inline istream& operator>>(istream&i,v(T)&v)

{rep(j,v.size())i>>v[j];return i;}

template<typename T>string join(const v(T)&v)

{stringstream s;rep(i,v.size())s<<' '<<v[i];return s.str().substr(1);}

template<typename T>inline ostream& operator<<(ostream&o,const v(T)&v)

{if(v.size())o<<join(v);return o;}

template<typename T1,typename T2>inline istream& operator>>(istream&i,pair<T1,T2>&v)

{return i>>v.fi>>v.se;}

template<typename T1,typename T2>inline ostream& operator<<(ostream&o,const pair<T1,T2>&v)

{return o<<v.fi<<","<<v.se;}

const double eps = 1e-6;

const ll LINF = 100200300400500600ll;

const int INF = 1001001001;

//--------------------------------------------------------

#define fastio cin.tie(nullptr); std::ios::sync_with_stdio(false);

#define myio ifstream iofi; if(argc>1){iofi.open(argv[1]); std::cin.rdbuf(iofi.rdbuf());}

#define myloopset int loop = 1; if(argc>2) loop =stoi(argv[2]); rep(i,loop)

//--------------------------------------------------------------

template <class T> T chmin(T &a,T b){if(a>b){a=b; return 1;}else return 0;}

template <class T> T chmax(T &a,T b){if(a<b){a=b; return 1;}else return 0;}

const int dx[4] = {0,1,0,-1};

const int dy[4] = {-1,0,1,0};



struct D21{

  int is,js;

  D21(int isize,int jsize){

    is = isize;

    js = jsize;

  }

  int operator()(int i,int j){

    return i*js+j;

  }

};





void Main(){

  int h,n;

  cin>>h>>n;

  vi a(n),b(n);

  rep(i,n){

    cin>>a[i]>>b[i];

  }

  int p = 1;

  vvi dp(n+1,vi(h+p,INF));

  rep(i,n+1) dp[i][0] = 0;

  rep(i,n) rep(j,h+p){

    chmin( dp[i+1][j], dp[i][j] );

    chmin( dp[i+1][min(j+a[i],h)], dp[i+1][j]+b[i] );

  }

  int ans = dp[n][h];

  srep(i,h+1,h+p){

    chmin(ans,dp[n][i]);

  }

  cout<<ans<<endl;

} int main(int argc,char** argv)

{fastio; myio; myloopset Main();}