#include <stdio.h> #include <math.h> #include <string.h> int main(){ int dp[200]; int count[200]; int n,m,k,s; int c[200],w[200]; int i,j,res; while(~scanf("%d%d%d%d",&n,&m,&k,&s)){ for(i=1;i<=k;++i) scanf("%d%d",&w[i],&c[i]); memset(dp,0,sizeof(dp)); memset(count,0,sizeof(count)); for(i=1;i<=k;++i){ for(j=c[i];j<=m;++j){ if(dp[j]>=dp[j-c[i]]+w[i]){ dp[j]=dp[j]; count[j]=count[j]; }else{ dp[j]=dp[j-c[i]]+w[i]; count[j]=count[j-c[i]]+1; } } } res=1000000; for(i=m;i>=0;--i){ if(dp[i]>=n){ if(count[i]<=s){ if(i<res) res=i; } } } if(m-res<0) printf("-1 "); else printf("%d ",m-res); } return 0; }