#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 rd_long() ({long _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define wt(v) ({ulong _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 rrep(v,e) for(typeof(e) v=e;v--;)
#define min(a,b) (a<=b?a:b)
#define chmax(v,a) (v=v>=a?v:a)

typedef unsigned long ulong;

long d[1001];

int main(){
	rd_init();
	int n=rd();
	d[0]=rd_long();
	int k=rd();
	rep(i,n){
		int t=rd();
		int b=rd();
		rrep(j,min(i+1,k)){
			long y=t==1?d[j]+b:d[j]*2;
			if(y>1000000000000000000){
				write(1,"-1",2);
				_exit(0);
			}
			chmax(d[j+1],y);
		}
	}
	wt1(d[k]);
	_exit(0);
}