/*
#include <stdio.h>
int main()
{
int f,A,B,C,D;
scanf("%d",&f);
switch(f)
{
case 100:
case 99:
case 98:
case 97:
case 96:
case 95:
case 94:
case 93:
case 92:
case 91:
case 90:printf("A");break;
case 89:
case 87:
case 86:
case 85:
case 84:
case 83:
case 82:
case 81:
case 80:
case 79:
case 78:
case 77:
case 76:
case 75:
case 74:
case 73:
case 72:
case 71:
case 70:printf("B");break;
case 69:
case 68:
case 67:
case 66:
case 65:
case 64:
case 63:
case 62:
case 61:
case 60:
case 59:
case 58:
case 57:
case 56:
case 55:
case 54:
case 53:
case 52:
case 51:
case 50:
case 49:
case 48:
case 47:
case 46:
case 45:
case 44:
case 43:
case 42:
case 41:
case 40:printf("C");break;
default:printf("D"); break;
}
return 0;
}
*/
#include <stdio.h>
int main()
{
int f,A,B,C,D,F;
scanf("%d",&f);
switch(f)
{
case 100:
case 99:
case 98:
case 97:
case 96:
case 95:
case 94:
case 93:
case 92:
case 91:
case 90:printf("A");break;
case 89:
case 87:
case 86:
case 85:
case 84:
case 83:
case 82:
case 81:
case 80:printf("B");break;
case 79:
case 78:
case 77:
case 76:
case 75:
case 74:
case 73:
case 72:
case 71:
case 70:printf("C");break;
case 69:
case 68:
case 67:
case 66:
case 65:
case 64:
case 63:
case 62:
case 61:
case 60:printf("D");break;
default:printf("F"); break;
}
return 0;
}