C++ :

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
long long int n,m;
long long int c[105][105],a[105],b[105];
bool f(long long int k)
{
	long long int maxy=-1;
	memset(c,-1,sizeof(c));
	c[0][0]=0;
	for(long long int i=1;i<=n;i++)
	for(long long int j=0;j<=m;j++)
	{
		maxy=-1;
		for(long long int l=max((long long)0,j-k/a[i]);l<=j;l++)
		{
			if(c[i-1][l]==-1) continue;
			maxy=max(c[i-1][l]+(k-(j-l)*a[i])/b[i],maxy);
		}
		c[i][j]=maxy;
	}
	if(c[n][m]>=m) return 1;
	return 0;
}
int main()
{
	long long int l,r,mid,i;
	scanf("%lld%lld",&n,&m);
	c[0][0]=0;
	for(i=1;i<=n;i++)scanf("%lld%lld",&a[i],&b[i]);
	r=1000000000;
	l=1;
	while(l<=r)
	{
		mid=(l+r)/2;
		if(f(mid)) r=mid-1;
		else l=mid+1;
	}
	printf("%lld\n",l);
	return 0;
}