#include <bits/stdc++.h>
using namespace std;
#define _ <<" "<<
#define sz(x) ((int) (x).size())
typedef pair<int, int> pii;
typedef long long ll;
#define debug(x) cout<<#x<<':'<<x<<endl;
typedef unsigned long long ull;
const int maxn=2e5+100;
typedef long double ld;
void solve(){
    ld x,y;
    cin>>x>>y;
    int n;cin>>n;
    ld l,r,f;
    ld sum=0;
    ld rr=y;
    for(int i=0;i<n;i++){
        cin>>l>>r>>f;
        sum+=(r-l)*f;
        rr-=(r-l);
    }
    sum+=rr;
    ld ans=x/sum;
    cout<<fixed<<setprecision(8)<<ans<<endl;
    
}
                    


int main(){
    solve();
}