#include<iostream>
using namespace std;
main(){
int c, v0, v1, a, l;
cin >> c >> v0 >> v1 >> a >> l;
int stcl = c;
int td = v0;
int day = 0;
while (c > 0) {
day++;
if (day == 1) c -= v0;
else c -= v0 + l;
if (c <= 0) break;
v0 = min(v0+a, v1);
}
cout << day << endl;
}
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