#include<bits/stdc++.h> using namespace std; int n,m,s,k,dp[205][205],a[105],b[105]; int main(){ while(cin>>n>>m>>k>>s){ memset(dp,0,sizeof(dp)); for(int i=1;i<=k;i++)cin>>a[i]>>b[i]; for(int i=1;i<=k;i++){ for(int v=1;v<=s;v++){ for(int u=b[i];u<=m;u++){ dp[v][u]=max(dp[v][u],dp[v-1][u-b[i]]+a[i]); } } } int flag=-1; for(int u=0;u<=m;u++){ for(int v=1;v<=s;v++){ if(dp[v][u]>=n){ flag=m-u; u=m+1; break; } } } cout<<flag<<endl; } }