#include <iostream>
#include <cstdio>

using namespace std;

int main(){
  unsigned long long A, B, C;
  scanf("%llu %llu %llu", &A, &B, &C);
  B *= C;
  if (B > A)
    printf("-%llu\n", B - A);
  else
    printf("%llu\n", A - B);

  return 0;
}