#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("YES");}else{puts("NO");}
#define MAX_N 200005

int main() {
    int a, b, c, d, e;
    cin >> a >> b >> c >> d >> e;
    b -= c;
    int x = 0;
    int ans = 0;
    srep(i,1,b*a+1){
        if(i == 0){
            x = d;
        }else if(i % 10 == 0){
            if(e <= x){
                x -= e;
            }
        }
    }
    cout << ans << endl;
    return 0;
}