//Was yea ra,rra yea ra synk sphilar yor en me exec hymme METAFALICA waath!
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2")
#include<bits/stdc++.h>
using namespace std;
#define rg register
#define ll long long
#define ull unsigned ll
#define lowbit(x) (x&(-x))
#define djq 1000000007
const short sint=0x3f3f;
const int inf=0x3f3f3f3f;
const ll linf=0x3f3f3f3f3f3f3f3f;
const double alpha=0.73;
const double PI=acos(-1);
inline void file(){
	freopen("ball.in","r",stdin);
	freopen("ball.out","w",stdout);
}
char buf[1<<21],*p1=buf,*p2=buf;
inline int getc(){
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,(1<<20)+5,stdin),p1==p2)?EOF:*p1++;
}
//#define getc getchar
inline ll read(){
	rg ll ret=0,f=0;char ch=getc();
    while(!isdigit(ch)){if(ch==EOF)exit(0);if(ch=='-')f=1;ch=getc();}
    while(isdigit(ch)){ret=ret*10+ch-48;ch=getc();}
    return f?-ret:ret;
}
inline int rdstr(char* s){
	char ch=getc(); int len(0);
	while(ch<33||ch>126) ch=getc();
	while(ch>=33&&ch<=126) (*s++)=ch,++len,ch=getc();
	return len;
}
#define ep emplace
#define epb emplace_back
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define it iterator
#define mkp make_pair
#define naive return 0*puts("Yes")
#define angry return 0*puts("No")
#define fls fflush(stdout)
#define rep(i,a) for(rg int i=1;i<=a;++i)
#define per(i,a) for(rg int i=a;i;--i)
#define rep0(i,a) for(rg int i=0;i<=a;++i)
#define per0(i,a) for(rg int i=a;~i;--i)
#define szf sizeof
typedef vector<int> vec;
typedef pair<int,int> pii;
struct point{ int x,y; point(int x=0,int y=0):x(x),y(y) {} inline bool operator<(const point& T)const{ return x^T.x?x<T.x:y<T.y; }; };
inline int ksm(int base,int p){int ret=1;while(p){if(p&1)ret=1ll*ret*base%djq;base=1ll*base*base%djq,p>>=1;}return ret;}
inline void pls(int& x,const int k){ x=(x+k>=djq?x+k-djq:x+k); }
inline int add(const int a,const int b){ return a+b>=djq?a+b-djq:a+b; }
inline void sub(int& x,const int k){ x=(x-k<0?x-k+djq:x-k); }
inline int inc(const int a,const int b){ return a<b?a-b+djq:a-b; }
inline void ckmn(int& x,const int k){ x=(k<x?k:x); }
inline void ckmx(int& x,const int k){ x=(k>x?k:x); }
inline void ckmn(ll& x,const ll k){ x=(k<x?k:x); }
inline void ckmx(ll& x,const ll k){ x=(k>x?k:x); }
//mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

namespace bigint{
	typedef vector<ll> bint;
	const int base=1<<30;
	inline void print(bint x){
		vec tmp; const int n=x.size();
		for(rg int i=0;i<n;++i) for(rg int j=0;j<9;++j) tmp.epb(x[i]%10),x[i]/=10;
		while(tmp.back()==0) tmp.pop_back();
		if(tmp.empty()) tmp.epb(0);
		const int m=tmp.size();
		for(rg int i=m-1;~i;--i) printf("%d",tmp[i]); puts("");
	}
	inline bint get(int x){ return bint(1,x); }
	inline bint operator+(const bint& x,const bint& y){
		const int lx=x.size(),ly=y.size(),n=max(lx,ly); bint z; z.resize(n);
		for(rg int i=0;i<lx;++i) z[i]+=x[i];
		for(rg int i=0;i<ly;++i) z[i]+=y[i];
		ll r=0,q=0;
		for(rg int i=0;i<n;++i) q=(r+z[i])/base,z[i]=(r+z[i])%base,r=q;
		while(r) z.epb(r%base),r/=base;   
		return z;
	}
}
using namespace bigint;
bint f[10005];
int n,m,deg[10005],dep[10005],tot,ord[10005];
ll a[10005];
vec e[10005];
signed main(){
	//file();
	n=read(),m=read();
	rep(i,n) a[i]=read(),f[i]=get(a[i]);
	rep(i,m){
		const int u=read(),v=read();
		e[u].epb(v); ++deg[v];
	}
	rep(i,n) if(!deg[i]) ord[++tot]=i;
	rep(i,n){
		const int x=ord[i];
		for(int y:e[x]){
			f[y]=f[y]+f[x];
			dep[y]=dep[x]+1;
			if(!--deg[y]) ord[++tot]=y;
		}
	}
	const int len=f[ord[n]].size();
	const int ans=dep[ord[n]]+(len-1)*30+__lg(f[ord[n]][len-1]);
	printf("%d\n",ans);
	return 0;
}
/*

*/