N,D=map(int, input().split())
PQ = [list(map(int, input().split())) for _ in range(N)]
DP = [[0]*N for _ in range(2*D)]
maxv1 = -10**12
maxv2 = -10**12
maxi = -1
nextv = -10**12
for i in range(N):
    DP[0][i]=-PQ[i][0]
    DP[1][i]=PQ[i][1]-PQ[i][0]
    if DP[0][i]>maxv1:
        maxv1 = DP[0][i]
        maxi = i
        nextv = maxv2
        maxv2 = DP[1][i]

    else:
        nextv = max(nextv,DP[1][i])
for d in range(2,2*D):
    if d%2==0:
        for i in range(N):
            if maxi==i:
                DP[d][i]=-PQ[i][0]+nextv
            else:
                DP[d][i]=-PQ[i][0]+maxv2
    else:
        maxv1 = -10**12
        maxv2 = -10**12
        maxi = -1
        nextv = -10**12
        for i in range(N):
            DP[d][i]=PQ[i][1]+DP[d-1][i]
            if DP[d-1][i]>maxv1:
                maxv1 = DP[d-1][i]
                maxi = i
                nextv = maxv2
                maxv2 = DP[d][i]
            else:
                nextv = max(nextv,DP[d][i])
ans = 10**12
for i in range(0,2*D,2):
    ans = min(ans,max(DP[i]))
print(ans)