#include <chrono>
#include <thread>
#include<bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
using namespace std;
using namespace __gnu_pbds;
#define T top()
#define E end()
#define PS push
#define Q queue
#define PP pop()
#define L0 (LL)0
#define V vector
#define ST stack
#define FI first
#define MAX 4e18
#define MIN -MAX
#define DQ deque
#define SZ size()
#define C clear()
#define B begin()
#define F front()
#define SE second
#define DL double
#define G getline
#define IN insert
#define endl "\n"
#define EM empty()
#define cnn continue
#define MD 1000000007
#define PSB push_back
#define PI acos(-1.00)
#define PPB pop_back()
#define PSF push_front
#define ub upper_bound
#define lb lower_bound
#define PPF pop_front()
#define CF cout.flush()
#define line cout<<endl
#define LL long long int
#define one cout<<1<<endl
#define zer cout<<0<<endl
#define PQ priority_queue
#define kth find_by_order
#define nil cout<<-1<<endl
#define N cout<<"NO"<<endl
#define NN cout<<"No"<<endl
#define Y cout<<"YES"<<endl
#define fndidx order_of_key
#define YY cout<<"Yes"<<endl
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#define MAU cout<<"Case "<<mau<<": "
#define SP(pre) fixed<<setprecision(pre)
#pragma GCC optimization ("unroll-loops")
#define MMAU cout<<"Case "<<mau<<":"<<endl
#define __lcm(A1,A2) (A1/(__gcd(A1,A2)))*A2
#define FAST ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define file freopen("input.txt","r",stdin);freopen("output.txt","w",stdout)
#define UOSMOY v.C;w.C;ww.C;uu.C;uo.C;vo.C;vu.C;ab.C;bc.C;cc.C;uuu.C;a.C;b.C;c.C;u.C
typedef tree<LL, null_type, less<LL>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
#define remembermeforcenturies using namespace std::chrono_literals;std::this_thread::sleep_for(-4611686018427387904ms);
V<LL>v,w,ab,bc;
set<LL>uo;
map<LL,LL>ww,cc,u;
V<pair<LL,LL> >uu,su;
map<LL,V<LL> >uuu;
map<pair<LL,LL>,LL> vo,vu;
map<LL,pair<LL,pair<LL,LL > > > vs;
priority_queue<LL,V<LL>,greater<LL> > moy;
LL dx[]= {-1,0,1,0,1,1,-1,-1};
LL dy[]= {0,1,0,-1,-1,1,1,-1};
LL dxx[]= {2,1,-1,-2,-2,-1,1,2};
LL dyy[]= {1,2,2,1,-1,-2,-2,-1};
LL dp[101][10001];
LL ar[10][10];
int main()
{
//  BRR;
//  file;
    FAST;
    char ch;
    string a,b,c;
    DL x,y,d,e,f,g,h;
    LL n,i,j,k,p,q,o,l,s,tt=1,m,t,z,aa,r=0;
//    cin>>tt;
    for(LL mau=1; mau<=tt; mau++)
    {
        UOSMOY;
        ordered_set os;
        remembermeforcenturies;
        cin>>n;
        k=0;
        l=0;
        for(i=1; ;i++)
        {
            l+=i;
            k++;
            if(l>=n)
            {
                cout<<k<<endl;
                break;
            }
        }

    }
    return 0;
    //IN
    //AL
}

/*************************************************************************
	> File Name: 1.cpp
	> Author: Knowledge_llz
	> Mail: 925538513@qq.com 
	> Blog: https://blog.csdn.net/Pig_cfbsl 
	> Created Time: 2020/10/11 22:45:26
 ************************************************************************/
#include<bits/stdc++.h>
#define For(i,a,b) for(register int i=(a);i<=(b);++i)
#define pb push_back
#define pr pair<int,int>
#define fi first
#define se second
#define LL long long
#define mk(a,b) make_pair(a,b)
using namespace std;
int read(){
	char x=getchar(); int u=0,fg=0;
	while(!isdigit(x)){ if(x=='-') fg=1; x=getchar(); }
	while(isdigit(x)){ u=(u<<3)+(u<<1)+(x^48); x=getchar(); }
	return fg?-u:u;
}
const int maxx=1e5+10;
int n,m,sum=0,cnt=0,mx,ans=1e9;
int w[10],tmp[10],s[10],dis[10],v[maxx],l[maxx];
int p[10]={0,1,2,3,4,5,6,7,8};
pr a[maxx];
bool cmp(pr x,pr y){
	if(x.fi!=y.fi) return x.fi<y.fi;
	return x.se>y.se;
}
int iso(int x){
	x=lower_bound(v+1,v+cnt+1,x)-v-1;
	return l[x];
}
int solve(){
	s[0]=0;
	For(i,1,n){ tmp[i]=w[p[i]]; s[i]=s[i-1]+tmp[i];  dis[i]=0;}
	For(i,2,n) For(j,1,i-1){
		dis[i]=max(dis[i],dis[j]+iso(s[i]-s[j-1]));
		if(dis[i]>=ans) return dis[i];
	}
	return dis[n];
}
	
int main()
{
#ifndef ONLINE_JUDGE
	freopen("input.in", "r", stdin);
	freopen("output.out", "w", stdout);
#endif
	int u1,u2;
	n=read(); m=read();
	For(i,1,n){ w[i]=read(); mx=max(w[i],mx);}
	For(i,1,m){
		u1=read(); u2=read();
		a[i]=mk(u2,u1);
		if(u2<mx){ printf("-1\n"); return 0; }
	}
	sort(a+1,a+m+1,cmp);
	v[++cnt]=a[1].fi; l[cnt]=a[1].se;
	For(i,2,m)
		if(a[i].se>l[cnt]){
			v[++cnt]=a[i].fi;
			l[cnt]=a[i].se;
		}
	do{
		ans=min(ans,solve());
	}while(next_permutation(p+1,p+n+1));
	printf("%d\n",ans);
	return 0;
}
