merchant.cpp: In function 'int main()':
merchant.cpp:48:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d%d%d", &N, &M, &K);
~~~~~^~~~~~~~~~~~~~~~~~~~~~
merchant.cpp:51:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%lld%lld", &buy[i][k], &sell[i][k]);
~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
merchant.cpp:56:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d%d%d", &a, &b, &c);
~~~~~^~~~~~~~~~~~~~~~~~~~~~