def main():
    import sys
    input = sys.stdin.read
    data = input().split()
    idx = 0
    
    N = int(data[idx])
    idx += 1
    M = int(data[idx])
    idx += 1
    C = int(data[idx])
    idx += 1
    
    A = list(map(int, data[idx:idx+N]))
    idx += N
    
    operations = []
    for _ in range(M):
        L = int(data[idx]) - 1  # converting to 0-based index
        idx += 1
        R = int(data[idx]) - 1
        idx += 1
        operations.append((L, R))
    
    # Compute the gain for each operation
    gains = []
    for L, R in operations:
        total = sum(A[L:R+1])
        gain = total - C
        gains.append(gain)
    
    # Sort operations based on the maximum gain
    sorted_ops = sorted([(gains[i], operations[i]) for i in range(M)], key=lambda x: (-x[0], x[1][0]))
    
    # Simulate the greedy selection
    current_state = [0] * N
    total_gain = 0
    included = []
    
    for gain, (L, R) in sorted_ops:
        # Calculate the actual gain if we include this operation
        actual = 0
        for i in range(L, R+1):
            if current_state[i] == 0:
                actual += A[i]
            else:
                actual -= A[i]
        actual -= C
        
        if actual > 0:
            total_gain += actual
            for i in range(L, R+1):
                current_state[i] ^= 1
            included.append((L, R))
    
    print(total_gain)

if __name__ == '__main__':
    main()