#include<cstdio>
const long long N=5e5+5,Mx=2e9;
long long n,m,K,l,r,Nr=0,o=1,ST,ED,st,ed,p,q,v,s=0,ans=0,Ans=0,D[N],F[N],NXT[N],LAST[N],NUM[N],A[N],Xr[N],Yr[N],d[N],nxt[N],num[N],last[N],c[N],w[N];bool vis[N];
long long Min(long long t1,long long t2){return t1<t2?t1:t2;}
void Add(long long t1,long long t2,long long t3,long long t4){
    o++;nxt[o]=t2;last[o]=num[t1];num[t1]=o;c[o]=t3;w[o]=t4;
    o++;nxt[o]=t1;last[o]=num[t2];num[t2]=o;c[o]=0;w[o]=0-t4;
}
long long ss(long long x,long long y){
    if(x==ed){ans+=y;Ans+=y*d[st];return y;}
    long long h=y,z;vis[x]=true;
    for(long long i=num[x];i;i=last[i]){
        if(h<=0)break;
        if(!vis[nxt[i]]&&c[i]>0&&d[nxt[i]]+w[i]==d[x]){
            z=ss(nxt[i],Min(c[i],h));
            h-=z;c[i]-=z;c[i^1]+=z;
        }
    }
    return y-h;
}
bool ll(){
    long long mi=Mx;
    for(long long i=1;i<=n;i++)if(vis[i])
        for(long long j=num[i];j;j=last[j])
            if(!vis[nxt[j]]&&c[j]>0&&d[nxt[j]]+w[j]-d[i]<mi)mi=d[nxt[j]]+w[j]-d[i];
    if(mi==Mx)return false;
    for(long long i=1;i<=n;i++)if(vis[i])d[i]+=mi;
    return true;
}
int main(){
    // freopen("ex_apers3.in","r",stdin);
    // freopen("ex_apers3.out","w",stdout);
    scanf("%lld %lld %lld",&n,&m,&K);scanf("%lld %lld",&ST,&ED);
    for(long long i=1;i<=n;i++)scanf("%lld",&A[i]),F[i]=Mx;F[ST]=1;
    for(long long i=1;i<=m;i++)scanf("%lld %lld",&Xr[i],&Yr[i]),NXT[i]=Yr[i],LAST[i]=NUM[Xr[i]],NUM[Xr[i]]=i;
    l=0;r=1;D[r]=ST;while(l<r){l++;for(int i=NUM[D[l]];i;i=LAST[i])if(F[D[l]]+1<F[NXT[i]]){F[NXT[i]]=F[D[l]]+1;r++;D[r]=NXT[i];}}if(F[ED]<K){printf("-1");return 0;}
    for(long long i=1;i<=K;i++,Nr+=n<<1){for(long long j=1;j<=m;j++)Add(Nr+Xr[j]+n,Nr+Yr[j],Mx,0);for(long long j=1;j<=n;j++)Add(Nr+j,Nr+j+n,A[j],0),i<K?Add(Nr+j,Nr+j+n*3,Mx,0):void();}
    st=Nr+1;ed=Nr+2;Add(st,ST,Mx,0);Add(ED+Nr-n,ed,Mx,0);n=Nr+2;
    do{
        do{
            for(long long i=1;i<=n;i++)vis[i]=false;
        }while(ss(st,Mx));
    }while(ll());
    printf("%lld",ans==Mx?-1:ans);
}