Unbearable Controversy of Being CodeForces - 489D

#include <bits/stdc++.h>
using namespace std;

struct node
{
int v;
int next;
};

node edge[30010];
int first[3010],book[3010];
int n,m,num;

void addedge(int u,int v)
{
edge[num].v=v;
edge[num].next=first[u];
first[u]=num++;
return;
}

int main()
{
int i,j,u,v,w,ans;
while(scanf("%d%d",&n,&m)!=EOF)
{
memset(first,-1,sizeof(first));
num=0;
for(i=1;i<=m;i++)
{
scanf("%d%d",&u,&v);
addedge(u,v);
}
ans=0;
for(u=1;u<=n;u++)
{
memset(book,0,sizeof(book));
for(i=first[u];i!=-1;i=edge[i].next)
{
v=edge[i].v;
for(j=first[v];j!=-1;j=edge[j].next)
{
w=edge[j].v;
if(w!=u)
{
book[w]++;
}
}
}
for(i=1;i<=n;i++)
{
ans+=(book[i]*(book[i]-1))/2;
}
}
printf("%d\n",ans);
}
return 0;
}