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

#define rd(v) long v=0;{long _c;while(_c=*rp++-48,_c>=0)v=v*10+_c;}
#define wt(v) {ulong _z=v;do*--wp=_z%10+48;while(_z/=10);}
#define rep(v,e) for(long v=0;v<e;++v)
#define chmax(v,a) (v=v>=a?v:a)

typedef unsigned long ulong;

long f1(){
	char*mmap();
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd(n);
	rd(m);
	long c=0;
	long d=0;
	rep(i,n){
		long b=0;
		rep(j,m){
			rd(a);
			b+=a;
		}
		chmax(c,d+b);
		chmax(d,c-b);
	}
	return c;
}

long f2(long z){
	char wbuf[64],*wp=wbuf+sizeof wbuf;
	wt(z);
	write(1,wp,wbuf+sizeof wbuf-wp);
	_exit(0);
}

int main(){
	f2(f1());
}