def main():
    import sys
    input = sys.stdin.read().split()
    idx = 0
    N = int(input[idx])
    idx += 1
    C = int(input[idx])
    idx +=1
    workers = []
    for i in range(N):
        a = int(input[idx])
        b = int(input[idx+1])
        idx +=2
        workers.append( (a, b) )
    
    min_total = float('inf')
    for i in range(N):
        a_i, b_i = workers[i]
        total = b_i
        total += a_i * N
        cost = 0
        for j in range(1, N+1):
            distance = abs(j - (i+1))  # i+1是岛的编号，从1到N
            cost += distance * C
        total += cost
        if total < min_total:
            min_total = total
    print(min_total)

if __name__ == '__main__':
    main()