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

#define getrp() ({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd_skip() while(*rp++>=48)
#define rd() ({long _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 MD 998244353

typedef unsigned long ulong;

ulong inverse(int a){
	int b=MD;
	int u=1;
	int v=0;
	int s,t;
	while(b){
		t=a/b;
		s=b; b=a-t*b; a=s;
		s=v; v=u-t*v; u=s;
	}
	if(u<0){
		u+=MD;
	}
	return u;
}

int main(){
	char*rp=getrp();
	rd_skip();
	unsigned m=rd();
	long b=0;
	ulong c=0;
	while(*rp){
		long a=rd();
		b=a-b;
		c=(c*(m-1)+a)%MD;
	}
	if(b%m){
		write(1,"-1",2);
	}else{
		char wbuf[64],*wp=wbuf+sizeof wbuf;
		wt((c*inverse(m)+1)%MD);
		write(1,wp,wbuf+sizeof wbuf-wp);
	}
	_exit(0);
}