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

#define rd_skip() while(*rp++>=48)
#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 rrep(v,e) for(long v=e;--v>=0;)
#define chmax(v,a) (v=v>=a?v:a)

char wbuf[1<<25];

int d[3000];

int main(){
	char*mmap();
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	rd_skip();
	long i=rd();
	while(*rp){
		long s=rd();
		int a=rd();
		rrep(j,i+1-s){
			chmax(d[j+s],d[j]+a);
		}
	}
	char wbuf[64],*wp=wbuf+sizeof wbuf;
	wt(d[i]);
	write(1,wp,wbuf+sizeof wbuf-wp);
	_exit(0);
}