#include<stdio.h>
#define GMax 1002
#define WMax 5002
FILE *f=fopen("energii.in","r");
FILE *g=fopen("energii.out","w");
int G,W,C[WMax][GMax];
struct generator{int e,c;};
generator A[GMax];

int min(int x,int y)
{if(x < y && x) return x;
else return y;
}

void Completare(int i,int j)
{int k,ok=0;
k=i-A[j].e;
if(k>=1){ if(C[k][j-1]) ok=1;}
else if(k==0) ok=2;
if(ok==2)
C[i][j] = min(C[i][j-1],A[j].c);
else if(ok==1) C[i][j] = min(C[i][j-1],A[j].c+C[k][j-1]);
else C[i][j] = C[i][j-1];
}

void Read()
{int i;
fscanf(f,"%d %d",&G,&W);
for(i=1;i<=G;i++)
	fscanf(f,"%d %d",&A[i].e,&A[i].c);
}

int main()
{int s=0,i,j;
Read();
for(i=1;i<=W;i++)
	C[i][1] = 0;
C[A[1].e][1] = A[1].c;
for(i=1;i<=G;i++)
	s+=A[i].e;
if(s < W) fprintf(g,"-1\n");
else
{
	for(i=1;i<=W;i++)
		for(j=2;j<=G;j++)
			Completare(i,j);
	fprintf(g,"%d\n",C[W][G]);
}
return 0;
}