#include <bits/stdc++.h> using namespace std; typedef signed long long ll; #undef _P #define _P(...) (void)printf(__VA_ARGS__) #define FOR(x,to) for(x=0;x<(to);x++) #define FORR(x,arr) for(auto& x:arr) #define FORR2(x,y,arr) for(auto& [x,y]:arr) #define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++) #define ALL(a) (a.begin()),(a.end()) #define ZERO(a) memset(a,0,sizeof(a)) #define MINUS(a) memset(a,0xff,sizeof(a)) //------------------------------------------------------- int N,M; ll C; ll A[101010],B[101010]; void solve() { int i,j,k,l,r,x,y; string s; cin>>N>>M>>C; FOR(i,N) cin>>A[i]; FOR(i,M) cin>>B[i]; sort(A,A+N); reverse(A,A+N); sort(B,B+M); x=0; ll sum=0; FOR(i,N) { while(x<M&&A[i]*B[x]<=C) x++; sum+=(M-x); } _P("%.12lf\n",sum/(1.0*N*M)); } int main(int argc,char** argv){ string s;int i; if(argc==1) ios::sync_with_stdio(false), cin.tie(0); FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin); cout.tie(0); solve(); return 0; }