def main():
    import sys
    input = sys.stdin.read().split()
    ptr = 0
    N = int(input[ptr])
    ptr +=1
    M = int(input[ptr])
    ptr +=1
    A = int(input[ptr])
    ptr +=1
    
    intervals_by_r = [[] for _ in range(N+2)]  # r can be up to N
    for _ in range(M):
        l = int(input[ptr])
        ptr +=1
        r = int(input[ptr])
        ptr +=1
        p = int(input[ptr])
        ptr +=1
        intervals_by_r[r].append( (l, p) )
    
    dp = [-float('inf')] * (N+1)  # since i ranges from 0 to N
    dp[0] = 0
    current_max = 0  # max dp[j] for j < i
    
    for i in range(1, N+1):
        cost = A if i != N else 0
        case_b = current_max - cost
        
        case_a = -float('inf')
        for (l, p) in intervals_by_r[i]:
            j = l -1
            if j >=0 and dp[j] != -float('inf'):
                temp = dp[j] + p - cost
                if temp > case_a:
                    case_a = temp
        
        dp_i = max(case_a, case_b)
        dp[i] = dp_i if dp_i != -float('inf') else 0  # Handle case where both are -inf
        
        if i != N:
            if dp[i] > current_max:
                current_max = dp[i]
    
    print(max(dp[N], 0))  # Ensure non-negative result as per problem's examples

if __name__ == '__main__':
    main()