genius

#include <cstdio>
const int maxn = 50001;
FILE *in = fopen("genius.in","r"), *out = fopen("genius.out","w");
struct graf
{
    int nod;
    graf *next;
};

int n,m,s,p,sol;
graf *a[maxn];
int v[maxn],c[maxn];

void add(int what, int where)
{
    graf *q = new graf;

    q->nod = what;
    q->next = a[where];
    a[where] = q;
}

void read()
{
    fscanf(in,"%d %d",&n,&m);
    int x,y;
    for (int i=0;i<m;++i)
    {
        fscanf(in, "%d %d", &x, &y);

        add(y, x);
        add(x, y);
    }
    fscanf(in,"%d %d",&s,&p);
}

void bfs()
{
    for ( int i = 1; i <= n; ++i )
        v[i] = -1;

    v[s] = 0;

    int p = 0, u = 0;
    c[p] = s;

    while ( p <= u )
    {
        int x = c[p++];

        graf *q = a[x];

        while ( q )
        {
            if ( v[q->nod] == -1 )
            {
                v[q->nod] = v[x] + 1;
                c[++u] = q->nod;
            }

            q = q->next;
        }
    }

    for ( int i = 1; i <= n; ++i )
        if(sol<v[i])
            sol=v[i];
}

int main()
{
    read();
    bfs();
    v[s]=1;
    for ( int i = 1; i <= n; ++i )
        if(v[i]==-1)
        {
            fprintf(out,"%d ",-1);
            return 0;
        }
    fprintf(out, "%d ",sol+p);
    return 0;
}