#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
#define maxn 100005
int n,m,s,k,tot;
int v[maxn];
long long ans;
inline int read(){char ch=getchar();int x=0,f=1;for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-1;for(;isdigit(ch);ch=getchar())x=x*10+ch-'0';return x*f;
}struct WW{int id,ad,has;
}w[maxn];bool cmp(WW a,WW b){return a.ad>b.ad;
}bool check(){for(int i=1;i<=n;i++)if(v[i]<k)return 0;return 1;
}int main(){freopen("express.in","r",stdin);freopen("express.out","w",stdout);n=read();m=read();s=read();k=read();//n家快递，m个数据，s天，增加k。for(int i=1;i<=m;i++){w[i].id=read();int x;x=read();w[i].ad=x-2;} sort(w+1,w+m+1,cmp);for(int i=1;i<=m;i++){int id=w[i].id;if(w[i].ad<0)continue;if(v[id]<k){v[id]+=w[i].ad;ans+=w[i].ad;w[i].has=1;tot++;}}if(!check()||tot>s){printf("-23333333\n");fclose(stdin);fclose(stdout);return 0;}sort(w+1,w+m+1,cmp);if(tot<s){for(int i=1;i<=m;i++){if(w[i].has||w[i].ad<0)continue;ans+=w[i].ad;tot++;if(tot==s)break;}}cout<<ans<<endl;fclose(stdin);fclose(stdout);return 0;
}

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 200005
using namespace std;int n,m,s,k,day;
int v[maxn];
long long ans;
struct WW{int id,ad,has;
}w[maxn];inline int read(){char ch=getchar();int x=0,f=1;for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-1;for(;isdigit(ch);ch=getchar())x=x*10+ch-'0';return x*f;
}bool cmp(WW a,WW b){return a.ad>b.ad;
}bool check(){for(int i=1;i<=n;i++)if(v[i]<k)return false;return true;
}int main(){n=read();m=read();s=read();k=read();//n个公司，m个数据，偷s天，每个增加kfor(int i=1;i<=m;i++){int x;w[i].id=read();x=read();w[i].ad=x-2;} sort(w+1,w+m+1,cmp);for(int i=1;i<=m;i++){int ad=w[i].ad,id=w[i].id;if(ad<0)continue;if(v[id]<k){day++;v[id]+=ad;w[i].has=1;ans+=ad;if(day==s)break;}}if(!check()){printf("-23333333\n");return 0;}if(day<s){sort(w+1,w+m+1,cmp);for(int i=1;i<=m;i++){if(w[i].has||w[i].ad<0)continue;ans+=w[i].ad;day++;if(day==s)break;}}cout<<ans<<endl;return 0;
}

//35分钟finish  reverse 只能对字符数组操作
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 500005
using namespace std;int js,top;
int vec[maxn];
char s[maxn];struct WW{int l,r;
}w[maxn];bool cmp(WW a,WW b){return a.l>b.l;
}int main(){freopen("unknown.in","r",stdin);freopen("unknown.out","w",stdout);cin>>s;int len=strlen(s);for(int i=0;i<len;i++){if(s[i]=='('){vec[++top]=i;}if(s[i]==')'){w[++js].l=vec[top--];w[js].r=i;}}sort(w+1,w+js+1,cmp);for(int i=1;i<=js;i++){int l=w[i].l,r=w[i].r;reverse(s+l,s+r+1);}for(int i=0;i<len;i++)if(s[i]>='a'&&s[i]<='z')printf("%c",s[i]);fclose(stdin);fclose(stdout);return 0;
}

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;vector<int>vec[22];
int n,m,k,ans;
int fa[22],d[22][22],tmp[22],v[22];int f(int x){return fa[x]==x?x:fa[x]=f(fa[x]);
}void change(int fx,int fy){for(int i=0;i<vec[fx].size();i++){int p=vec[fx][i];tmp[i]=p;}for(int i=0;i<vec[fy].size();i++){int p=vec[fy][i];vec[fx].push_back(p); }for(int i=0;i<vec[fx].size();i++){vec[fy].push_back(tmp[i]); }return;
}
int main(){freopen("prison.in","r",stdin);freopen("prison.out","w",stdout);scanf("%d%d%d",&n,&m,&k);ans=n;for(int i=1;i<=m;i++){int x,y;scanf("%d%d",&x,&y);d[x][y]=d[y][x]=1;}for(int i=1;i<=n;i++)fa[i]=i,vec[i].push_back(i);for(int i=1;i<=n;i++){for(int j=1;j<=n;j++){int fx=f(i),fy=f(j);if(fx==fy)continue;        int sum=0;for(int p=0;p<vec[fx].size();p++){int g=vec[fx][p];if(d[j][g]&&g!=i)sum++;}for(int p=0;p<vec[fy].size();p++){int g=vec[fy][p];if(d[i][g])sum++;}if(sum+v[fx]+v[fy]<=k){fa[fx]=fy;v[fy]+=sum+v[fx];ans--;    change(fx,fy);if(ans==1){printf("1\n");fclose(stdin);fclose(stdout);return 0;}break;}}}printf("%d\n",ans);fclose(stdin);fclose(stdout);return 0;
}