#include <iostream>
#include <fstream>
#include <stdio.h>
#include <string.h>

using namespace std;
typedef pair<char, char> pcc;
const int Nmax = 105;
const int Lmax = 105;

int N, L;
int B[Nmax][2];
//int dp[Lmax][Lmax];
int dp[Lmax];
int nt[Lmax];
pcc from[Lmax][Lmax];

inline int min(int x, int y) { return x < y ? x : y; }
inline int max(int x, int y) { return x > y ? x : y; }

bool check(int T)
{
    memset(dp, -1, sizeof(dp));
    dp[0] = 0;
    for (int n = 0; n < N; n++)
    {
        int a = B[n][0];
        int b = B[n][1];
        for (int l = 0; l <= L; l++)
            nt[l] = -1;
        int x = 0;
        while(x*a <= T)
        {
            int y = (T - x*a) / b;
            for (int l = 0; l < L; l++)
                if (dp[l] >= 0)
                {
                    if (l+x <= L && nt[l+x] < dp[l] + y)
                        nt[l+x] = dp[l] + y;
                    else if (l+x > L && nt[L] < dp[l] + y)
                        nt[L] = dp[l] + y;
                }
            x = max(x+1, (T - (y-1)*b)/a);
        }
        for (int l = 0; l <= L; l++)
            if (dp[l] < nt[l])
                dp[l] = nt[l];
        if (dp[L] >= L)
            return 1;
    }
    return 0;
}

int main()
{
    ifstream f ("lapte.in");
    ofstream g ("lapte.out");
    
    f >> N >> L;
    for (int n = 0; n < N; n++)
        f >> B[n][0] >> B[n][1];
    
    int low = 1, high = 205*L;
    while(low < high)
    {
        int mid = (high +low)/2;
        if (check(mid))
            high = mid;
        else
            low = mid +1;
    }
    g << low << '\n';


    return 0;
}