// O(N * log(N) + (D + N) * log(|max_ans|)) time solution

#include <stdio.h>

#define N_MAX 1000
#define D_MAX 1000
#define P_MAX 100000

typedef struct {
	int key, id;
} data;

void merge_sort(int n, data x[])
{
	static data y[N_MAX + 1];
	if (n <= 1) return;
	merge_sort(n / 2, &(x[0]));
	merge_sort((n + 1) / 2, &(x[n/2]));
	
	int i, p, q;
	for (i = 0, p = 0, q = n / 2; i < n; i++) {
		if (p >= n / 2) y[i] = x[q++];
		else if (q >= n) y[i] = x[p++];
		else y[i] = (x[p].key < x[q].key)? x[p++]: x[q++];
	}
	for (i = 0; i < n; i++) x[i] = y[i];
}

void chmax(long long* a, long long b)
{
	if (*a < b) *a = b;
}

int main()
{
	int i, N, D, P[N_MAX + 1], Q[N_MAX + 1];
	data d[N_MAX + 1];
	scanf("%d %d", &N, &D);
	for (i = 0; i < N; i++) scanf("%d %d", &(d[i].key), &(d[i].id));
	merge_sort(N, d);
	for (i = 0; i < N; i++) {
		P[i+1] = d[i].key;
		Q[i+1] = d[i].id;
	}
	P[0] = 0;
	Q[0] = -P_MAX;
	
	const int sup = P_MAX + 1;
	int j, argmax[N_MAX + 1][3] = {}, argmax_inv[N_MAX + 1][3][2] = {};
	for (i = 1; i <= N; i++) {
		for (j = 0; j < 3; j++) argmax[i][j] = argmax[i-1][j];
		j = argmax[i-1][0];
		if (Q[i] - P[i] > Q[j] - P[j]) {
			argmax_inv[i][0][0] = P[i];
			argmax_inv[argmax[i][0]][0][1] = P[i] - 1;
			argmax_inv[argmax[i][0]][1][0] = P[i];
			argmax_inv[argmax[i][1]][1][1] = P[i] - 1;
			argmax_inv[argmax[i][1]][2][0] = P[i];
			argmax_inv[argmax[i][2]][2][1] = P[i] - 1;
			argmax[i][2] = argmax[i][1];
			argmax[i][1] = argmax[i][0];
			argmax[i][0] = i;
			continue;
		}
		j = argmax[i-1][1];
		if (Q[i] - P[i] > Q[j] - P[j]) {
			argmax_inv[i][1][0] = P[i];
			argmax_inv[argmax[i][1]][1][1] = P[i] - 1;
			argmax_inv[argmax[i][1]][2][0] = P[i];
			argmax_inv[argmax[i][2]][2][1] = P[i] - 1;
			argmax[i][2] = argmax[i][1];
			argmax[i][1] = i;
			continue;
		}
		j = argmax[i-1][2];
		if (Q[i] - P[i] > Q[j] - P[j]) {
			argmax_inv[i][2][0] = P[i];
			argmax_inv[argmax[i][2]][2][1] = P[i] - 1;
			argmax[i][2] = i;
		}
	}
	argmax_inv[argmax[N][0]][0][1] = sup;
	argmax_inv[argmax[N][1]][1][1] = sup;
	argmax_inv[argmax[N][2]][2][1] = sup;

	long long l = 1, r = (long long)D * P[2], m, dp[D_MAX + 1][4], tmp;
	int h, k[D_MAX + 1][4], x, last[4][2];
	while (l < r) {
		m = (l + r) / 2;
		
		for (j = 0; j < 3; j++) {
			dp[0][j] = -1;
			k[0][j] = 0;
			last[j][0] = -1;
			last[j][1] = -1;
		}
		dp[0][3] = m;
		for (k[0][3] = 0; k[0][3] < N && P[k[0][3] + 1] <= m; k[0][3]++);
		last[3][0] = 0;
		last[3][1] = -1;
		
		for (i = 1, dp[0][3] = m; i <= D; i++) {
			for (j = 0; j < 4; j++) dp[i][j] = -1;
			for (j = 0; j < 4; j++) {
				if (k[i-1][j] == 0) continue;
				
				for (h = 0; h < 3; h++) {
					x = argmax[k[i-1][j]][h];
					if (h == j || x == 0) continue;
					tmp = dp[i-1][j] - P[x]; 
					if (tmp < 0) continue;
					else tmp += Q[x];
					
					if (argmax_inv[x][0][0] <= tmp && (argmax_inv[x][0][1] == sup || tmp <= argmax_inv[x][0][1])) chmax(&(dp[i][0]), tmp);
					if (argmax_inv[x][1][0] <= tmp && (argmax_inv[x][1][1] == sup || tmp <= argmax_inv[x][1][1])) chmax(&(dp[i][1]), tmp);
					if (argmax_inv[x][2][0] <= tmp && (argmax_inv[x][2][1] == sup || tmp <= argmax_inv[x][2][1])) chmax(&(dp[i][2]), tmp);
					if (!(argmax_inv[x][0][0] <= tmp && (argmax_inv[x][0][1] == sup || tmp <= argmax_inv[x][0][1])) && !(argmax_inv[x][1][0] <= tmp && (argmax_inv[x][1][1] == sup || tmp <= argmax_inv[x][1][1])) && !(argmax_inv[x][2][0] <= tmp && (argmax_inv[x][2][1] == sup || tmp <= argmax_inv[x][2][1]))) chmax(&(dp[i][3]), tmp);
				}
			}
			if (dp[i][0] + dp[i][1] + dp[i][2] + dp[i][3] == -4) break;
			
			for (j = 0; j < 4; j++) {
				if (dp[i][j] < 0) continue;
				else if (last[j][0] < 0) {
					for (k[i][j] = 0; k[i][j] < N && P[k[i][j] + 1] <= dp[i][j]; k[i][j]++);
					last[j][0] = i;
				} else if (last[j][1] < 0) {
					for (k[i][j] = 0; k[i][j] < N && P[k[i][j] + 1] <= dp[i][j]; k[i][j]++);
					last[j][1] = i;
				} else {
					if (dp[i][j] > dp[last[j][0]][j] && dp[i][j] > dp[last[j][1]][j]) break;
					else if (dp[last[j][0]][j] > dp[last[j][1]][j]) {
						if (dp[i][j] <= dp[last[j][1]][j]) for (k[i][j] = k[last[j][1]][j]; k[i][j] > 0 && P[k[i][j]] > dp[i][j]; k[i][j]--);
						else for (k[i][j] = k[last[j][0]][j]; k[i][j] > 0 && P[k[i][j]] > dp[i][j]; k[i][j]--);
						last[j][0] = i;
					} else {
						if (dp[i][j] <= dp[last[j][0]][j]) for (k[i][j] = k[last[j][0]][j]; k[i][j] > 0 && P[k[i][j]] > dp[i][j]; k[i][j]--);
						else for (k[i][j] = k[last[j][1]][j]; k[i][j] > 0 && P[k[i][j]] > dp[i][j]; k[i][j]--);
						last[j][1] = i;
					}
				}
			}
			if (j < 4) {
				i = D + 1;
				break;
			}
		}
		
		if (i > D) r = m;
		else l = m + 1;
	}
	printf("%d\n", -l);
	fflush(stdout);
	return 0;
}