C :

int main()
{int n,a,b,c;
scanf("%d",&n);
a=n/500;b=n%500/5;
    c=1000*a+5*b;
    printf("%d",c);
    
}

C++ :

#include <bits/stdc++.h>
#define int long long
#define pb push_back
#define fer(i,a,b) for(int i=a;i<=b;++i)
#define der(i,a,b) for(int i=a;i>=b;--i)
#define all(x) (x).begin(),(x).end()
#define pll pair<int,int>
#define et  cout<<'\n'
#define xx first
#define yy second
using namespace std;
template <typename _Tp>void input(_Tp &x){
    char ch(getchar());bool f(false);while(!isdigit(ch))f|=ch==45,ch=getchar();
    x=ch&15,ch=getchar();while(isdigit(ch))x=x*10+(ch&15),ch=getchar();
    if(f)x=-x;
}
template <typename _Tp,typename... Args>void input(_Tp &t,Args &...args){input(t);input(args...);}
vector<pll> v;
const int N=1e6+10;
signed main(){
    int n;
	input(n);
	int ans=0;
	ans+=n/500*1000;
	n%=500;
	ans+=n/5*5;
	cout<<ans;
}

Python :

# coding=utf-8
s=int(input())
print((s%500)//5*5+(s//500*1000))