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#include <bits/stdc++.h>
#include <random>
#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
#define ff first
#define dd second
#define mp make_pair
#define lld long long
#define pb emplace_back
#define sz size()
#define For(i,s,a) for(int i=(int)s;i<(int)a;++i)
#define pii pair<int,int>
#define pll pair<lld,lld>
#define rpt(S,it) for(auto it=S.begin();it!=S.end();++it)
#define mod (lld)(1e9+7)
#define scanf(...) scanf(__VA_ARGS__)?:0
#define P first
#define S second
#ifdef __WIN32__
#define gcx getchar
#elif __linux__
#define gcx getchar_unlocked
#endif
#define piii pair<pii,pii>
//template<typename T>
#define T int
inline void scan(T *i)
{
	register T t=0;
	register char z='a';
	register bool neg=0;
	while(z<'0' || z>'9'){if(z=='-')neg^=1;
	z=gcx();}
	while(z>='0' && z<='9')
	{
		t=(t<<3ll)+(t<<1ll)+z-'0';
		z=gcx();
	}
	if(neg)t=~(t-1);
	*i=t;
}

vector<int>c[301],rc[301];
int ts[301],_end;
int dp[311];

void dfs(int x)
{
	dp[x]=1;
	For(i,0,c[x].sz)if(!dp[c[x][i]])
	dfs(c[x][i]);
	ts[--_end]=x;
}

lld get(lld a)
{
	int tmp=0;
	For(i,0,a)
	tmp=max(tmp,dp[ts[i]]);//cout<<dp[ts[i]]<<" ";puts("");
	return tmp;
}

void det(lld allowed, lld alt, lld a)
{
	For(x,0,a){dp[ts[x]]=1;
	For(i,0,rc[ts[x]].sz)
	dp[ts[x]]=max(dp[ts[x]],dp[rc[ts[x]][i]]+1);
	if(dp[ts[x]]>=allowed && alt)
	dp[ts[x]]=-1,--alt;}
}

void ran(lld allowed, lld alt, lld a)
{
	For(x,0,a){dp[ts[x]]=1;
		For(i,0,rc[ts[x]].sz)
		dp[ts[x]]=max(dp[ts[x]],dp[rc[ts[x]][i]]+1);
		lld cha=rand()%100+1;
		if((dp[ts[x]]-allowed)>-2)
		cha+=20;
		//if(ts[x]==1 || ts[x]==5)cha=100;else cha=0;
		if(cha>100 && alt)//cout<<ts[x]<<" "<<allowed<<" "<<alt<<endl,
		dp[ts[x]]=-1,--alt;
	}	
}

lld rec(lld tries, lld all, lld alt, lld a)
{
	lld ret=1000000000;
	memset(dp,0,sizeof(dp[0])*(a+2));
	det(all,alt,a);
	ret=min(ret,get(a));
//	puts("");
//	cout<<all<<" "<<alt<<" "<<a<<endl;
//	tries=0;
//	tries=10;
	while(tries--)
	{
		memset(dp,0,sizeof(dp[0])*(a+2));
		ran(all,alt,a);
		ret=min(ret,get(a));
	}
	return ret;
}

bitset<301>used;

void sdet(int a)
{
	memset(dp,0,sizeof(dp[0])*(a+2));
	For(x,0,a)
	if(used[ts[x]])dp[ts[x]]=-1;
	else
	{
		dp[ts[x]]=1;
		For(i,0,rc[ts[x]].sz)
		dp[ts[x]]=max(dp[ts[x]],dp[rc[ts[x]][i]]+1);
	}
}

void brut(lld a, lld b, lld d)
{
	lld wyn=1000000;
	if(d==1)
	{
		For(i,1,a+1){
			used=0;
		used[i]=1;
		sdet(a);
		wyn=min(wyn,get(a));
	//	cout<<get(a)<<endl;
		}
	}
	else
	if(d==2)
	{
		For(i,1,a)
		For(j,i+1,a+1)
		{
			used=0;
			used[i]=used[j]=1;
			sdet(a);
			wyn=min(wyn,get(a));
		}
	}
	else
	if(d==3)
	{
		For(i,1,a-1)
		For(j,i+1,a)
		For(k,j+1,a+1)
		{
			used=0;
			used[i]=used[j]=used[k]=1;
			sdet(a);
			wyn=min(wyn,get(a));
		}
	}
	else
	if(d==4)
	{
		For(i,1,a-2)
		For(j,i+1,a-1)
		For(k,j+1,a)
		For(l,k+1,a+1)
		{
			used=0;
			used[i]=used[j]=used[k]=used[l]=1;
			sdet(a);
			wyn=min(wyn,get(a));
		}
	}
	printf("%lld",wyn);
}

int main()
{
	srand(69692137);
	int a,b,d,g,h;
	scan(&a),scan(&b),scan(&d);
	For(i,0,b)scan(&g),scan(&h),c[g].pb(h),rc[h].pb(g);
	_end=a;
	For(i,1,a+1)
	if(!dp[i])dfs(i);
	if((d==4 && a<60) || (d==3 && a<140) || (d<3))
	{
		brut(a,b,d);
		return 0;
	}
	lld minx=a;
	lld tries=20000000ll/((a)*a);
	For(i,1,a+1)
		minx=min(minx,rec(tries,i,d,a));
	printf("%lld",minx);
}
 
 /*
 5 6 2
 1 2 1 3 1 4
 2 5 3 5 4 5
 */