#include <stdio.h>
int main(void)
{
    int A,B,C,D,E,F;
    scanf("%d %d %d %d %d",&A,&B,&C,&D,&E);
    if(D <= E)
    {
        F=A-B;
        printf("%d\n",F);
    }
    else
    {
        F=A-B+C*D-C*E;
        printf("%d\n",F);
    }
    return 0;
}