原代码

#include<bits/stdc++.h>
using namespace std;
int gcd(int a,int b)
{
  return a%b==0?b:gcd(b,a%b);
}
int lcm(int a,int b)
{
  return a*b/gcd(a,b);
}
int main()
{
  int a,b,c;
  cin>>a>>b>>c;
  cout<<1+(a-1)*b/lcm(b,c);
  return 0;
}

wa记录 新代码

#include<bits/stdc++.h>
using namespace std;
#define lint long long
lint gcd(lint a,lint b)
{
  return a%b==0?b:gcd(b,a%b);
}
lint lcm(lint a,lint b)
{
  return a*b/gcd(a,b);
}
int main()
{
  lint a,b,c;
  cin>>a>>b>>c;
  cout<<1+(a-1)*b/lcm(b,c);
  return 0;
}

ac记录 真是不开longlong见祖宗啊