#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

#define rd_init() char*rp=({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd() ({int _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define wt(v) ({unsigned _z=v;do*--wp=_z%10+48;while(_z/=10);})
#define wt1(v) ({char wbuf[64],*wp=wbuf+sizeof wbuf;wt(v);write(1,wp,wbuf+sizeof wbuf-wp);})
#define rep(v,e) for(typeof(e)v=0;v<e;++v)
#define repeat(e) for(typeof(e)_=e;_--;)

int b[200000];

int main(){
	rd_init();
	int n=rd();
	int t=rd();
	rep(i,n-1){
		int a=rd();
		b[i]=t-=a;
	}
	if(t>0){
		write(1,"0",1);
		_exit(0);
	}
	int k=rd();
	int c=0;
	repeat(k){
		int x=rd();
		if(c+b[x-2]<=0){
			goto dame;
		}
		c+=10;
	}
	if(c+t<=0){
		dame:;
		write(1,"-1",2);
	}else{
		int z=-t/10u+1;
		wt1(z);
	}
	_exit(0);
}